What we're talking about is very controversial. They are very old terms - like from 16th-17th centuries - and I don't think many modern astrologers bother with this concept. I don't. I believe it was used in Horary Decumbitures in regard to health and healing William Lily wrote about it).
I also think that the astrologers back then had a whole different way of looking at astrology. If one of them were here explaining it to us, from their view, maybe it'd make some sense. Mercury in health astrology could mean many things - trouble with nerves, would be one.
They didn't keep birth time records back then, so they had to use horary. We have birth charts now and so we have a different system to use. In modern health astrology, Mercury could point the finger at the nervous system still, but it is so much more complicated than that (in my opinion).
Do any of you have a difficult time thinking or processing information or doing any of Mercury functions with your Sun-Mercury conjunction? If the answer is no - don't worry about it. I have Mercury conjunct Mars which is also suppose to be bad for Mercury. I suppose it might, in the sense that often I want to express something in a short time - get it all out at once - and I do have that feeling. But, it is tempered by other planets. I can sit and write and take my time, even if I have the sense of hurry that Mars brings. Mars also gives me passion. So, you see - it's how you use your conjunctions that matters.
From an internet astrology glossary:
- A planet is combust when it is in conjunction with the Sun and therefore hidden from sight by the light of the Sun. Traditionally this is a serious debility and implies that the planet is weakened or restricted in power. However, if the planet is within 17 minutes of the Sun, it is termed Cazimi - in the heart of the Sun - and considered strengthened by the union.
In his Introduction, William Lilly stated that the combust planet should be in the same sign as the Sun and within 8° 30' - beyond this distance, but within 17 ° of the Sun, the planet is said to be under the Sun's beams. This condition is debilitating, but not as severe as combustion.
Compubst, Cazmini, and under the Suns Beams were established long ago to use in Horary. Lilly - was a health astrologer and wrote of this:
"The significator of the Querent combust, shows him or her in great fear, and overpowered by some great person". (CA., p.113)
However, later, in his horary volume, (p.300): he also writes:
A Planet within 12 degrees of the Sun, is said to be under his Beames, and then hath not fortitude, let it be in what Signe it will; when a Planet is within 16 minutes of the Sun, he is said to be in Cazimi, or heat of the Sun, and then it's an addition of fortune, and he is wonderous strong.
That aphorism was no doubt translated from the work of an older author, but it appears to acknowledge the controversy regarding whether a planet can be combust when in a different sign to the Sun.