I guess solitary confinement in prison does not count because the C.O. goes bye to count and bring your food.
But if that does not count, I spent 72 days in the hole in 98 when I was Tahachapi Prison. It was an awful lot of solitude and all I did was read books and sleep.
That time in the hole gave me the time to think about getting my head out of my ass so I would not have to go back to prison anymore. Been off parole since Jan 2000 and do not get in to trouble anymore because I do not drink alcohol or do drugs, only weed and that is legal here.