Does anyone else ever do something and later can't figure out why?

Does anyone else ever change and look back at something they have done and can't believe that they did it? I mean, it's kind of like I have several personalities, though they all answer to the same name and have the same past they react distinctly different to situations. One day I'll laugh at what another day I will lose my temper over. The worst part is when I do something thinking I'm being completely rational and justified and then a few days later I'll realise that the 'jerk' who had a go at me or said I wasn't being fair or something similar was actually in the right and I can't fathom why I would have imagined that the things I said or did were justifiable... I've actually burnt bridges and hurt people I've cared about like this. At the time I feel they are hurting me and later I realise that the only pain I feel is the shame and guilt for the way that I acted. Unfortunately it's not always possible to apologise - you can't undo the past... So am I alone in this? Do others also shift and change, reacting one way on a certain day and then days later (or it could be as short as hours later) realise that you have no idea why you would act in such a way?