I would think they needed to go to the dr and be prepared to keep going back, if necessary. (Unless there was an obvious reason, like having very noisy neighbors waking them up at night or they were just staying up all night, either for work or hobbies etc)
If they were going to bed at night and sleeping as well, it could be some kind of health complaint.
Someone sleeping so much could be a symptom of M.E., but there would be other symptoms, too, like general pain, feeling very hot or cold, feeling flu-ish, getting worse a day or so after exertion, mixing up words, short term memory problems, sore throats etc.
The poor research on and attitudes to M.E, has resulted in some doctors having a very odd view of 'fatigue' , and sometimes a very dismissive attitude, to tiredness type symptoms, especially in women.
If someone gets an M.E cfs diagnosis, they need to be very proactive about doing their own research on the subject, and being sure they fit the description. The forum 'phoenix rising', for example , would have information on it, or Tymes Trust for kids.
M.E is a really serious condition,but some drs don't see it as that, at all. There is a danger that if they once diagnose it, they stop looking for other things.
Which can be a real problem ,because sleeping a lot can be a symptom of other things.
When my daughter was in her early 20s , she came down with an aggressive cancer . (She's fine now, we were very lucky and it was caught in time, and she's more than 5 years symptom free, now.)
The first symptom she and any of us noticed was a lump- that's what she went to drs with, but I only realized after she'd been diagnosed, and II read about sudden unexplained tiredness being potentially a cancer symptom- that we remembered how much she'd being sleeping, before she got ill.
For a few months before she was diagnosed, she was sleeping more and more, we just didn't know- we thought it was things like being at work full time, after being a student. She wasn't depressed, she looked well. but -when we looked back, we remembered her saying, 'I lay down for a minute and then I woke up 2 hours later', or 'I just watched a dvd and I was asleep before 10' I wish I had realized it was something that should have been making me worry more, but it built up rather gradually and somehow , we didn't realize it was a problem
- and she was close enough to the teenage lie-ins age, it didn't seem particularly odd.
Hopefully, it isn't anything like this, in the case you mention-but I did want to write about this, because cancer detection in the uk is not good-it often takes quite a lot of visits , to get a referral-but it's a condition you need to be quick with, and it can make a big difference.(Particularly ,in the uk cancer detection , in young people isn't very good)
When you get to a hospital, with the right consultant, care is often very good, my daughter's was fantastic, and we were and are really grateful for it.
it can be, getting a gp to agree to refer you, where the delays happen. (as well as people not even knowing they should go to a dr, of courses, as well).
Basically, sleeping that much needs checking out, could be liver diabetes, depression M.E.or maybe iron deficiency or b12, etc.
Anyway sorry for writing such a long post, and I hope your sleepy person is ok :)