Dee,
I've actually been thinking about that myself. I'm thinking it was habit. I was in a bar and people drink in bars and I've generally always drank in bars.
I went to this bar a couple of months ago and didn't drink. But that time I made sure I was aware before I went that I wouldn't drink. This time I just went and without thinking much ordered alcohol. In fact when I was asked what I wanted I wasn't sure (as I haven't been drinking) so I had time and opportunity to choose something nonalcoholic.
I went to 4 bars and in the last bar I was by this time really drunk but I was caught up in the occasion and wanted the night to continue. The people in the bar immediately brought and opened a bottle of wine for me as this is what I always drank there. I knew there was no way I was in a state to drink it and even tried to protest but it seemed to go over their head.
I know we've all been there but this feeling of despair really is emotionally crippling.