Oh my... I do the exact same thing at work. My work involves a lot of standing (I'm a part time usher at a theatre) and... well it's just really embarrassing when a patron has to wake you up cuz you've fallen asleep standing up.

Do you have a tendency to fall asleep everywhere? I don't know, but I have never had an issue falling asleep, and I fall asleep almost everywhere, especially in moving cars/subways. The only advice I can offer you is, since caffeine doesn't work, cut back on it and maybe THAT could help, or just fight through it. And enjoy the trippy dreams that come with constantly living half passed out.