I was having the same issues as your son, which began for me at 23. I was falling asleep while driving to work, at work, coming home from work, immediately after work, wake up long enough to eat dinner, then would go directly to bed. I've done a couple of sleep studies and they call what I have Idiopathic Hypersomnia- which means excessive day time sleepiness. It's not narcolepsy, because I don't lose my muscle control and don't dream during the short sleeping spells. I now take 2 different pills each morning to get me through the day. I stopped taking the meds when I was pregnant and then while I was nursing. My boss thought I was severely depressed and hated life alltogether, because I looked horrible- always very tired and moved kind of slow.
As far as the sleep study itself, they're not very fun. I guess that might depend on where you go, but each time I've had mine, they put electrodes attached to wires all over my head, face, and chest. I also had to sleep with a tube directly under my nose to monitor my oxygen intake. There was also a monitor clip on my finger. I had to go to a facility for both. I stayed over night, but also had to do a nap study- so I stayed the next day as well and had to take 20 minute naps every 2 hours. After a "restfull" night's sleep, I was falling alseep during the naps withing 1-2 minutes each time.
I know meds like I take are a mother's worst nightmare and they don't want to go that route, but don't eliminate the option if the results are that the doctor recommends them. They have changed my life for the better, and I can excel in what I do now, rather than struggle to stay awake and focus.
Good luck!!