HERMIT
A person who has withdrawn to a solitary place for a life of religious seclusion
Any person living in seclusion; recluse
The synonyms are words with which I am not familiar. Are you?
Eremite
Monastic (that word I AM familiar with)
Anchorite
Cenobite
Both.
Some people choose a solitary life (usually for religious reasons). Some people who are hermits have mental problems (not in their right mind). Still others end up alone by circumstances, such as - being very shy, have trouble interacting with others (don’t “fit in”), were abused (physically, mentally, sexually), and so forth. People like this usually end up being ostracized or ignored as others don’t know how to deal with them (considered odd).
Yes, they can “go mad”. Loneliness (whether real or perceived) is a form of torture.
Shuhak 