heya...i was just browsing the forums and saw your post, so i figure what better time to join and post when i can relate to what you're talkin about!
when i was about 16 (i'm 23 now) i experienced my first panic attack ever. it was pretty emotionally scarring i think. i was sitting in class and all of a sudden my neck got sore and i thought i tasted copper in my mouth and all the things i knew about strokes / seizures made me freak out. my blood pressure was 220/120 when the school nurse took it, i ended up in the e.r. and hopsital. for about 8 hours i thought i was going to die. probably about the most disturbing incident anyone can experience, definitely life-changing. a few weeks after that, since i was convinced it had to be something with my brain, i started obsessing over a brain tumor / something else (even tho they took a CT scan and w/e other tests that revealed it to be nothing else)
while i was obsessing over the fact it could be a brain tumor, i did a lot of the"spacing out" you describe and i would realize i was spaced out and that would cause me to have short little panic attacks (like 5 minutes). it felt like i was constantly spacing out. and it just gets worse and worse because i thought my spacing out was caused by a brain problem when my spacing out was really just me thinking about my brain! it's a pretty crappy cycle that's really hard to break. i don't really have a fear of a brain tumor anymore because if i had one i'd probably be dead by now
unfortunately for me, my panic attacks have gone away but now i have become a hypochondriac and experience wicked anxiety from it(any strange sensation i experience, that was probably there but i never took notice before my first panic attack, is some life-threatening debilitating health issue)
i wish i had some advice for you to make it better but really for me the only thing that helped with the brain tumor fear was time, even tho i had tests that showed nothing wrong. this disorder sucks