I like people and everything, however, every now and then I really like spending time alone.
Me too. Spending too much time in isolation can lead to depression though
That is true.  However, there are benefits to solitude.  It allows for self reflection, inner growth and focusing on self concept
Yeah, as long as you keep your mind busy, any negative affects can be avoided
Then on the other side of things, there is the idea of solitary confinment, such as in prisons. I like solitude, but only when it is my choice
Yeah, solitary confinement is a pretty harsh punishment beyond incarceration 
Yes I would imagine being locked in solitary confinment would do a number on you mentally.  
Being isolated for that long can lead to anxiety and sensory illusions