I've felt that way at various times. I dunno about your case, but mine's a reaction to being treated as though invisible, dominated by people who have more outgoing personalities or sometimes deliberately dominated by control freaks. I finally started standin' up for myself.
Hey, you're not invisible. Whether it's just a current lack of available friends to communicate with, or whether you're in a worse state of mind, please be assured you're a valid person at all times.
And hey, if you have God inside you, you're never alone. That, I've found to be true and trustworthy no matter what.