Typically when something manifests to the degree you are describing, it is because there are multiple factors with potential to cause it (that is why some of the general this in that sign info doesn't apply - there are no supporting factors). In your chart, I see several indications.
Your Sun and AC positions, in themselves, would not cause this feeling, but help explain why it manifests in this way, and how it can become so overwhelming before
The AC is referred to as the mask, or the face we put on to the world. It also shows how we feel we should act, or present ourselves. The Leo AC can create a feeling that you should be confident, proud and extroverted. The ruler of your AC is the Sun.
Your Sun is in Taurus - a sign noted for patience, strength and determination. On the flip side (less positive attributes), Taurus can be slow, immobile, and inflexible. In other words, the immobilized feeling is Taurus dig-in-your-heels and patiently wait until you're sure - manifesting to an extreme. As mentioned above, the Sun's placement in the 10th house increases the importance of image, or how people in general view you.
The two strongest factors I see as the underlying cause are Neptune and Pluto. Feelings similar to this are quite common with 6th house Neptune/ 4th house Pluto (it isn't to uncommon of combination, as Neptune and Pluto are around 60 degrees apart in the chart of every living person, so Pluto is often 1-3 houses behind Neptune 2 houses being most common).
The 6th house relates to service, responsibility, and obligation. Overwhelming, vague feelings of guilt are CLASSIC of 6th house Neptune. With your 6th in Saturn-ruled Capricorn, this can become a repressive tunnel-vision effect, with a singular focus on meting obligations, and a constant guilty feeling that those obligations are not met. With Saturn, ruler of the 6th falling in the 7th house of the Other - the obligations you feel constantly plagued by may be a direct result of the expectations of the Other. Saturn is also the planet that, in his most negative expression, whispers in your ear "Don't try. If you don't try, you can't fail" In his positive expression he is whispering "Don't try - do it. Failure is irrelevant - continue on despite any and all obstacles" He is unbending, either immense determination to do nothing, or to do exactly what you set out to do.
The Neptune-Uranus conjunction in your 6th serves to further complicate matters. Uranus is a freedom seeking planet, where he falls there is an inherent desire for flexibility and individuality. You very likely have a secret desire to throw all of your obligations, responsibilities, and the people who impose them right out the window. It seems, from what you've said, that the Uranian energy is repressed here, so those secret desires probably only result in further guilt - as if it were proof you aren't living up to expectations, because somewhere deep down you don't want to.
Your 6th house planets form a loose square to both Venus and Mercury in your 9th. Venus is the planet of relations with other people. The square from Venus can result as real and/or imagined desires of others applying pressure with the force of Aries. The "humble servant" 6th house Neptune is very receptive to this kind of pressure. The square to Mercury may cause a feeling of obligation to respond to the requests of others, and/or difficulty achieving clarity in communication (can't find the right words when you want to stick up for yourself). The Neptune sextile to Pluto naturally makes these 6th house Neptune effects go hand-in-hand with the 4th house Pluto effect.
Wherever Pluto falls in your chart is a difficult point - not being a naysayer, I love Pluto but he's difficult. Pluto relates to depth, darkness, and intensity. Yours in strong (your entire generation has a strong Pluto for this reason) because he is in his own sign of Scorpio.
The 4th house is the house of home, roots and childhood. This placement usually indicates something dark you experienced of witnessed as a child had a profound effect. There could have been a lack of attention/affection or harsh repercussions for misbehavior that made the impression early on you must meet others approval/expectation to be loved. This may not have been anything done to you deliberately - situations such as the death of a loved one, or moving away from friends can feel like punishment to a small child.
In emotional/psychological/spiritual matters the 4th house still relates to the concept of roots. This is your deepest, most private emotions, desires and fears. What you are not even consciously aware of and what has not fully developed lie in the 4th house. I once read an excellent description of the 4th as the core of the psychological onion. If you began peeling away what is right on the surface - clear in your conscious mind and apparent to others- and continued peeling a layer at a time until you reached the very center - you would be in the 4th house.
One of the classic effects of Pluto in the 4th is that feeling "there is something wrong with me, deep down, and they will hate me if they ever find out". With your fourth house cusp also in Scorpio, there is an intense need for privacy - at least of your very deepest self. This feeling as if you have a monster lurking deep in your soul is often ignored, avoided, and therefore repressed. You can never look at it honestly, and see if (I bet the answer is no) there is any reason to feel this way if you're afraid to ask yourself why.
Another significant factor is Jupiter - ruler of your Moon in opposition to your Moon. This typically exaggerates stress, fear, guilt - all of those challenging emotions are expanded by Jupiter.
There is one more factor I would like to discuss, which in the big picture, is probably the most important. If you don't believe in reincarnation, disregard this last bit.
Your North Node is in Capricorn, in the 5th house forming a quincunx to Chiron in your 12th. The North Node is the only one (typically) shown on a chart, but it's always exactly opposite of your South Node. The South Node represents past lives; lessons, challenges, and karmic connections you brought with you. There have no doubt been many more experiences and effects from past lives, but this point shows us what of them is manifesting in this life. The South Node is, in a way, a comfort zone. On a level beyond conscious memory, this is what you're used to. In the spirit of growth, evolution, and progress your soul is driven to move beyond that, into uncharted territory. It may be easier to re-live the past, you've had some practice, but to grow you move away from it.
The North Node shows the aim of your soul in this incarnation. It is what challenges you've chosen to take on, lessons you need to learn. It is frightening, because it feels foreign. It also feels exciting, like you are driven to move in this direction. Your North Node in the 5th house indicates you need to learn to take a chance. This is the house ruling gambling, and risk-taking. In past lives you were probably a leader, respected and well accepted in society; mature and careful. Now you are faced with the challenge of taking a risk.
Let your inner child play, learn how to express yourself. If you fail, you learn a lesson and move on. If others don't like it, it's their problem. This is the spirit of the 5th, and the direction your soul was heading as you entered this incarnation. It is also a foreign and frightening change from the way you lived before.
As far as how to handle it - learning to understand your birth chart is the best first step you can make. You are very right that understanding is the key to coping.
(expansion, also wisdom) as the "handle". So you need to understand things before you do them. The challenge is it is impossible to fully know everything before you do it and anything you do will have something in it that you only learn about AFTER you do it. So learn all you can before doing something and, at some point, decide you have ENOUGH information, and begin doing it.
