There are, of course, many reasons for a seizure in adults.
Your friend might want to have an EEG and a brain wave scan.
If your friend is a flyer he will possibly have to inform the CAA of his misfortune and also the DVLA. The DVLA has quite a good medical information section which you can access on the internet. I suspect that he may find himself off driving for a year.
I believe that some medications can cause a fit, and also, giving up the sauce, after some time 'on' the stuff, can also produce a fit grand mal or petit mal. The grand mal is, I think rather the more serious of the two types and may be characterized by unconsciousness, tongue biting, incontinence and general confusion upon waking.
I think that you will find that there is much information on the net.
Two of my friends hve recentl had such an experience. In one case the seizure was due to stress and overwork. In the other, the cause was rather more serious. The first has returned to an absolutely normal life after a period of medication. The second is on his way to recovery.
I should add that this information comes from layman, not a medical practitioner of any sort.
With best wishes for his speedy recovery.