Biblically speaking (which is, at least, generally historically correct) they were treated as though they were demon possessed and therefore outcast.
I am not sharing this as an attempt to convert or preach to anyone, it's just an example of mental illness before it was recognized as such:
Possible trigger:
Jesus Restores a Demon-Possessed Man
5 They went across the lake to the region of the Gerasenes.[a] 2 When Jesus got out of the boat, a man with an impure spirit came from the tombs to meet him. 3 This man lived in the tombs, and no one could bind him anymore, not even with a chain. 4 For he had often been chained hand and foot, but he tore the chains apart and broke the irons on his feet. No one was strong enough to subdue him. 5 Night and day among the tombs and in the hills he would cry out and cut himself with stones.
6 When he saw Jesus from a distance, he ran and fell on his knees in front of him. 7 He shouted at the top of his voice, “What do you want with me, Jesus, Son of the Most High God? In God’s name don’t torture me!” 8 For Jesus had said to him, “Come out of this man, you impure spirit!”
9 Then Jesus asked him, “What is your name?”
“My name is Legion,” he replied, “for we are many.” 10 And he begged Jesus again and again not to send them out of the area.
11 A large herd of pigs was feeding on the nearby hillside. 12 The demons begged Jesus, “Send us among the pigs; allow us to go into them.” 13 He gave them permission, and the impure spirits came out and went into the pigs. The herd, about two thousand in number, rushed down the steep bank into the lake and were drowned.