Not at all uncommon, especially among pilots in their late twenties and early thirties, will even admit to suffered a twinge or two of it myself in that age bracket. Seen it countless times to varying degrees in airline trainees of mine. The worst case I saw was a captain friend on 'heavies' who abandoned his career because of it, became so sick of himself in his self imposed grounding that he went back to airline ops and became chief pilot of a national carrier!
The one odd common thread in all cases was that the sufferers seemed to be of above average intelligence and flying ability.
Now the good part - In each and every case time was the healing factor, never less than a few months, and never more than 2 or 3 years. During a lengthy attachment which I had in training, the company's consulting psychologist referred a few deeply troubled souls to a hypno-therapist, this seemed to achieve good results.
Tell your friend to hang in there, do the responsible thing and stay on the ground if it really is all a bit too much for the moment, time is a great healer for this problem.