I have described to my psychiatrist how there have been occasions I have 'blacked out' in reaction to a fearful situation. Actually, 'whiting out' is a better description. This has happened at times I have reacted to a threatening situation with a bone-jarring fear. At these times I have been convinced I was going to die. I 'white out' (yes, things go white). I come to discovering I have lost time. (it is humiliating wondering how long I stood there and if I did anything during that time). He has suggested this is dissociation. I don't know much about it but is this something common with PTSD?

[MtnTime2896]

I can't offer statistics, but that happens to me when things get really bad. I've dissociated anywhere from a minute (or less) to two and half hours, at a time. It was normal for me ten months ago to do that. It happens a lot less often now but still occurs under extreme stress where I truly feel in danger (which can just be from an overwhelming flashback).

[MommaD]

Yes it's my understanding that disassociation is very common with ptsd. It's a coping mechanism when fear/memories/feelings become completely overwhelming. It's also kind of the reasons that treating ptsd is so hard--it's hard to deal with and process stuff you push away so thoroughly.
Sorry for the long answer, but yes, it is common in ptsd. If you're seeing a therapist please do mention it to them--there are some ways to help with this response and still keep from being overwhelmed.
Virtual hugs coming your way

[skeksi]

It's whiting out for me, too!