Everyone has bad days or weeks, when the feelings take over. Its part of what you are dealing with and I think it is healthy to feel them as they hit you.
When I am in such a place, I give myself permission to feel them for a few days (a weekend works for me!) and just let it all out. I think the key for me is to have a plan to snap out of it once I have released them so I don't stay in that place too long. For example, over a weekend, by Sunday afternoon, I will make sure I do some sort of enjoyable exercise, give myself a facial or something, and wear some clothes I feel good in.
I will also think of the three things that have been hitting me hardest, and come up with a positive mantra for each one for when I go there again. I won't bother using them till Monday, but they are ready at least! I will then watch some sort of happy movie and work out a way to get to sleep ok that night.
It won't morph me back straight away, but puts me on a better path at least, which is a good enough goal for me at that time.
If I can't snap myself out of a bad zone in a couple of days (by at least feeling better each day than the day before), then I will talk to a friend who will help me work out if I should do something more formal.
These periods seem to happen to me when I have been doing ok, then get several hits in a short period of time. I do always notice a greater feeling of detachment and peace when I do reach the other side, so hang in there!