While OR's reply is really helpful (and funny enough, because I was in the same situation as you were in when I was graduating school and I followed pretty much OR's suggestion, weight lifting, taking up guitar and a rec basketball league and generally not stress out and enjoy life and it worked really well ... for awhile until my old depression/anxiety came back), I feel that they are topical medication to much more deep-rooted issues.

Although most don't admit it, graduation from college is a scary experience; some sees as a transition into the real world, prepared or not, an evaluation for what they have achieved during college, if they have made up for their disappointments in high school or a continuation of the disappointments, or as a crystal ball to determine the future (e.g., a 4.0 GPA in CS/Econ leads to job at Goldman Sachs or Bio to Harvard Medical School, to a respectable life); Or "I didn't make any lasting friends or relationships, I'll be a loser for the rest of my life," or that I have found my niche, geek bent for SF conventions/hipsters bent for bohemian gentrifying neighborhood/prep bent for loft in a upscale yuppie neighborhood.

The reason most people can't commit to relationships or friendships are rooted in their own insecurity; either a feeling of inferiority/superiority when in company of others, e.g., "Lisa thinks that I'm cool, but she doesn't know who I truly am, just my pomped-up version of myself in the two times I did her" or "Fuck Dan, what does he know? He went to an arts school". It could also be that you aren't sure about what you want yourself, "Should I focus more on startup's or my social life? Should I climb the corporate ladder or pursue my own personal vision?"; Unclear personal visions leads confusion to whom you want to associate with and the values that you want to see in your friends/significant others.

Add it on top of that is your expectations that come with your startup dream. What do you wish it to validate? Because most human endeavors, when you boil down to it, isn't about money. And also, it probably isn't one of those vague feel-good mantras, "make a difference in the world, " "to innovate," or "to push envelope." The reason, most of the time is pretty personal, hence the term, "the revenge of the nerds." Why do you want to pursue your startup? So that you could be the next Sergey Brin and get invited to your high school/college graduation as a and say "fuck you" to everyone in the audience, to get the girl (or the boy), to prove your parents or former best friend or ex-girlfriend, or to correct something in the unspoken rules in the current mainstream social conventions that has hampered/traumatized you.

Answer these questions and don't resist it if they lead to paths totally different than pursuing startup's. Although most people don't like to admit it, pursuing startup's is like pursuing medicine. In the beginning, the prospect is exciting and promises the riches and respectability; it is only later that most people realize that becoming a doctor haven't solved all of their personal problems and just brought on a whole slew of more professional problems.

So, don't go to medical school unless you can't imagine doing anything but medicine.