SOLVED. Science Fiction - Alien parasite inside brain, acts as companion, able to control body (i.e. regrow limbs). [s]

[David]

I read this Science Fiction sometime around 1978-1981 or so. It is about a man who enters a cave and has an alien fall on him. The alien becomes a parasite inside his mind and acts as a companion to him. It has the ability to control some of his bodily functions, i.e. grow a new limb or internal organs, to keep him safe.

[Lou]

Needle?

[Kym]

Healer by F. Paul Wilson?

[David]

Thanks! It has been 40 years, so my memory of it was fuzzy at best, but this was Needle and it's sequel, Through the Eye of a Needle, by Hal Clement.