Usually I've found it's a feeling like other unpleasant feelings so I distract myself (with reading or working on an interest or project) and the feeling passes. You can only concentrate on one thing at a time so focusing on something else helps me get through a period of time where there are feelings that are uncomfortable.

I found that going out and talking to at least one person; store clerk, librarian, another customer at a store, etc. keeps me much more centered and not quite so introspective. I use to have trouble especially on weekends when there wasn't work or other ways of meeting/talking to people. So I quickly learned to just go out to the store or someplace "public" where I could chat with someone for a moment, see the "world" going on and be part of it.