Harvestlion,
No, you shouldn't be worried. Deal with it constructively, proactively. If you stay scared you cannot be in charge and will only be reactive, which is a recipe for making this worse not better.
If you are experiencing foggy brain that long, there is a physical cause. Get to it and take care of it. Planets don't do that 'to us' through some distant mystery mechanism. They are energetic principles that work through material mechanisms in/around the body.
I have experienced numerous Saturn square natal Mercury transits. The principle is this: You must let go of thinking patterns or patterns of communication in relation to others that are impairing you with negativity, cynicism and doubt. It may be this is coming from within yourself, not necessarily from others' words. But be sure. Say goodbye to anything/anyone that is inserting doubt/negativity into your mindset.
Another principle is that this is a period in which our ignorance gets exposed. We develop problems that require us to learn through conscious effort so that we can solve a problem that we initially do not even understand well enough to properly define.
Also, identify any possible physical toxins/environmental factors that may be contributing to/causing your brain fog. These things do not develop in a vacuum. If you have Mercury amalgam fillings in your teeth, make sure they are not breaking down. There are indicators for that. Consider possible lead and/or aluminum poisoning. Throw out any cooking vessels made of aluminum. Make sure you are not getting poisoned by your home's water supply. Put a filter on your tap. Airborne toxins are possible too, but look at all possible sources. Get help with this. Your brain fog will not allow you to do it all yourself and be effective.
In other words, do not wait trying to 'figure out' what this is within astrological analysis. Take decisive practical steps now in being proactive. You will not know the answer(s) at first, but taking charge and getting help will get you closer and closer.