I too was going to recommend you looking into wether he does drugs or not. I am a Vegetarian and I certainly do not loose weight like that at all. He really needs some help for his issue indeed.
Cindy
i was thinkin same thing as terry
My husband, children and I are all healthy vegans with stable weights. We are neither under nor overweight. As with any kind of diet, you must watch what you eat and do it right to acquire good health.
When my son lost over 60 lbs., staying awake for days at a time, starting art projects, sewing, etc. it was because he was using speed. He would sleep 18 to 24 hours because his body was completely wiped out from the speed run he just came down from. Find a source/support group for people who love and live with drug users. All of the symptoms you describe are consistent with speed use. If I am wrong, and I hope I am, I sincerely apologize. If you were never a drug user, it probably is harder to recognize it in others. God Bless. Get in touch with Narc Anon or Al Anon, people who are co-dependents with users, alcoholics, etc.