23 year old panic attacks

While people often feel as if they're about to black out during a panic attack actually doing so is uncommon, so I wouldn't be dismissing your son's loss of consciousness as just a panic attack symptom, Vanessa. This needs to be checked out.

Which is not to suggest a serious cause. It might be as simple as him not eating properly, or failing to breath, or even hyperventilating during the attack. But, better to be safe than sorry, IMHO.

If your son isn't being treated for panic disorder than he needs to consider getting help. Both psychotherapies and medication can be very effective, especially when treatment begins soon after the onset of symptoms. However, if panic attacks persist for more than a month or so then the disorder is unlikely to resolve of its own accord and mostly things get worse over time.

Best wishes

Ian

As Ian noted, blacking out could be an indication of something else. I suffer from Bipolar Disorder and I have blacked out at least a half a dozen times over the last five years, each time it was during a manic induced panic attack. It's scary when you black out, especially when you cannot remember what you have done. 

But there is help out there, again as Ian noted psychotherapy and medication are great ways to help. However, before you and your son go down this path,  I would suggest doing some due-dilligence; there is a tremendous amount of information on the internet that could help with your son's progress. 

Stay strong and I hope your son feels better,

 Dave.