Campbell’s Feb 1831 description of Rigdon:
“…His instability I was induced to ascribe to a peculiar mental and corporeal malady, to which he has been subject for some years. Fits of melancholy succeeded by fits of enthusiasm accompanied by some kind of nervous spasms and swoonings which he has, since his defection, interpreted into the agency of the Holy Spirit, or the recovery of spiritual gifts, produced a versatility in his genius and deportment which has been increasing for some time.
I was willing to have ascribed his apostacy to this cause, and to a conceit which he cherished that within a few years, by some marvelous interposition, the long lost tribes of Israel were to be collected, had he not declared that he was hypocritical in his profession of the faith which he has for some time proclaimed. Perhaps this profession of hypocrisy may be attributed to the same cause.
This is the only hope I have in his case.”
“In the accident, he [Sidney] received such a concussion of the brain as ever afterward seriously affected his character, and in some respects his conduct. His mental powers did not seem to be impaired, but the equilibrium of his mental exertions seems thereby to have been sadly affected. He still manifested great mental activity and power, but to an equal degree was inclined to run into wild and visionary views on almost every question.”
Van Wagoner, p. 117