Is seclusion a sign of mental instability?

I am noticing that I have an increased desire to stay at home by myself and sleep. I don't like doing things that I used to enjoy and I am not answering my phone as much as I used to. I also park my car a few streets down so that it will look like I am not home when ppl ride by. I don't know why I am doing this but it is starting to scare me.