what just happened

So I am having a test in one of my classes on Monday. My teacher was nice enouph to have a study session tonight to help prepare for it. So far not to bad. There was a total of 75 to 100 students there.  My teacher came in the room and explained how the session was going to work. There was going to be 2 parts.  The first part was the students were going to divide themselves up into groups og 6 to 8 people. This is where it went bad.  In this situations, I usually wait until someone asks me for me to be in their groups. Sometimes, rarely though, I go up to someone and ask.  For some reason, neither of the 2 happened.  I didn't know what to do, so I grabbed my stuff and left.  Thank God I was sitting in the back so it wasn't that noticeable. This is the first time that I remember leaving a situation like this.  I don't know if I should go see a psychiatrist or what.  Will it get worse or was this one of those time? I don't know what to do or who to talk to.