I hear you completely. If anything, I think this stage is the worst part of being bipolar. I always have the tendency
to hide out when things start going south. It's really bad, especially when people have no idea what's going on. In the last year, I've really alienated alot of pretty good friends by completely disappearing for about 3 months. Most of my close friends from the past though, are very busy with work, and recognize that we won't be in contact for extended periods of time. However, with my neighbors this past year, it was obvious that I was around at times and didn't contact them.
It's a tough time, because when you tell people they often don't understand. Even if they try to be there, most people don't really want to hear about all of your problems for extended periods of time when it goes sour. Hence the solution, hiding out. I know this is not a good thing but cannot break the cycle. As a fairly outgoing person, I find it impossible to be around people who know me when I'm not depressed. The funny thing is, they really don't see my manic phases as anything really too abnormal.
Anyway, I believe you have to do what you have to do. I would rather alienate people who don't understand and hold this against you as opposed to letting them see you in shambles. You won't feel bad about this until you start to feel better anyway. It can be very frustrating to try and extend yourself too at this point, and I've had too many people say "What happened? You used to be so much fun".
Tough time, but don't give up. The best thing to do is probably tell people what's happening the best you can and then disappear if you have to. Atleast then, they will have known prior to the problem occuring and jumping back into life will be easier when you get better. Not telling anyone can be dangerous, and often people will think you are just making excuses for your behavior when explaining after it's over.