You're most likely dissociating which is you used to cope during tramatic event and after. I think it's quite related to the avoident symptoms in PTSD. It's not really that you are forgetting, it's that your mind drifts off. Mine usually goes no where. What I mean is that my mind becomes blank. Some people dissociate into the actual event, or a made up life or an alter. But Typo's alert idea is also likely. I know when I've been in my alert mode, I can't think of anything else, but watching out to make sure nothing is close that will hurt me and my son.

I always forget what I'm doing, what I'm looking for, something I needed, but left at home. I'm always losing things. I used to use a St. Anthony candle, but I can't find that either haha. Sometimes I forget when I put this outfit on. For some mysterious reason this bag of clothes keeps getting up on my bed. I lay down everynight wondering how it got up there and I put it on the floor.

You can take this quiz called the Dissociative Experiences Scale: http://counsellingresource.com/quizzes/des/index.html It says it's for DID, but it is really about dissociative experiences in general.