This has happened to me many times. Don't let it frighten you - you won't go crazy. I remember how many times I had to remind myself of that when going through the "unreality" phases. When I feel this way, I worry that I'll permanently become "unattached" from the real world and go crazy, but you can be assured, that no one suffering from panic disorder has gone crazy. Sometimes I feel like I'm floating outside my body, or that I'm just going through the "motions" of life without really being "attached" to my body.
Don't worry, we all go through it. Sometimes it lasts a few hours, sometimes just one day. For me, the longest it's lasted is about a week. So hang in there, it'll be over before you know it.
