I'm not proud to admit this, but I am probably one of the most suitable individuals on the Steem blockchain to answer this question, due to the fact that I once spent 6 months in solitary confinement, as a result of a jail fight, that ended badly for the attacker (after unconvincingly telling the jail guards a PTSD laden Veteran should not be in general population).
As a result of my self defense ending in a hospitalization, they were prepared to finally move me out of general population, to a cozy cell, all by myself, for 6 months.
I do not feel it was bad for my mental health, any more so, than being confined to a facility. Quite the opposite for me. I will explain how I dealt with my time in solitary.
There may be a couple of things I am not remembering as well, but this was pretty much how I dealt with it. It was not easy by any means, but the mind is powerful. I was able to meditate and stay busy in cell, for 6 months. There was never a moment of boredom. I would create entertainment, and cognition.
The important aspect here is the insight I had into myself, and the situation. I really did feel hopeless at times, and felt as though it would never end, but I knew it would, so long as I could utilize my intelligence to maintain more friends than enemies. I knew this was an important factor.
I am a highly introverted person according to the Briggs/Myers personality test. INFJ, which accounts for a very small percentage of people. As an introvert. I am content while I am alone, and actually function better. I can only deal with people in small doses. To live in an environment like this is pure torture for someone like me. I have not gone back to jail since. Introverts learn their lessons quickly. I am terrified to even consider ever going through this again.
Why am I talking about introversion?
Because this is a major factor in how an individual will deal with such a setting. I was actually much more comfortable in confinement, than general population. When the 6 months was complete, I actually begged the guards to let me stay in confinement! Yes, it sounds insane, but I felt much safer, and knew that the variables to catastrophe were significantly reduced by my confinement.
The man I injured came close to death. This reaction happened because I was in fear for my life, and suffering from extreme PTSD. I had expressed this danger and concern, and it went ignored. If the man would have died, I would be serving a life sentence. I had 6 long months to consider this, and I didn't want these variables present if I could control my locale.
I started thinking of creative ways to go back to confinement without hurting anyone, or causing too much trouble, but they knew what I was up to, and told me it was not happening. I succumbed to the idea that I must become a mental chess player, and I made it out of there in one piece.
An extroverted person would likely have a different story to tell here.
Whether or not anyone agrees with this, confinement is a traumatizing experience, in my opinion. Some individuals deserve to rot in a cell, some individuals make mistakes and learn from them. I like to believe I am the latter. Having been a hopeless jailed drunk, to an aspiring writer, who is ambitious and productive, it shows that anything is possible if the will is present. We have the ultimate power to change the course of our lives.
It all starts with a willing decision to change.
I hope your friends who have dealt with confinement, are better people today as a result of their struggle, and not more damaged than when they went in.
I hope my answer helps.
Being alone and confining yourself is one of the things that must be done by humans, but only in a short time. This is a manifestation of the way humans know themselves deeper, and change to be good.
However, when solitude / solitary activities are carried out for too long, there are various adverse effects that can occur namely:
1. Decreasing Mental
Of course, most solitude will limit yourself from interacting with the outside world and other people. This will make yourself inferior to the strengths of others. And chain effects will continue to occur when after feeling inferior, you decide to keep confining yourself.
2. STRESS !!
Stress will arise when there is no one we can talk to / confide in. This will get worse when your bad thoughts overwhelm and tell you to commit a crime.
3. Decreasing Health
Of course, confining yourself will cause stress, and this is not good for your health. Stress, life patterns (eating, sleeping, etc.) that are not healthy, will cause a truly real disease.
In addition, there are still a series of bad effects that can even result in a bad death if you keep confining yourself. So, as much as possible, whatever your mind is, don't be alone for too long. Your mentality becomes unhealthy, so does your body.
We rely on feedback from other people to retain the integrity and sanity of our thought processes. We need others for perspective. Keeping a diary or expressing our thoughts in words can help us gain control of ourselves if we have difficult issues to work through. That works because creating an external reference of any kind can help us ground our thoughts. If you have no opportunity to interact with anyone or if you voluntarily isolate yourself from other people, your ideas may grow out of proportion - negative ideas in particular.