I'm going through a lot of exactly the same thing at the moment, though sans startup environment. I'm intrigued to read that you consider the root cause to be extroversion. I wouldn't call myself an extrovert at all, and would ascribe most of what you write about to anxiety (for which I've recently started seeing a CBT counsellor).
Do you think that having your coworkers available in-person would have changed things because 1) having them around would have "recharged your batteries", i.e. the extrovert theory, or 2) having them around would have added the pressure to counterbalance the procrastination (my situation a lot of the time), or 3) something else?