I'm glad you came to PC, and asked about your son. I am a high school teacher, and it's so good that he's seeing the school counselor. Have you also spoken to that person, and expressed your concerns? (They cannot tell you what your son has said, due to confidentiality, but, you can express your concerns and give that counselor a "head's up" so to speak.)
Also, (and please do not take this the wrong way), but, you mentioned a falling out with friends and school work falling off. Those are two signs of *possible* drug use. Have you considered this at all? I ask this question with all sincerity and with love in my heart for you and your son. My own son started using drugs in high school, and I was unaware. He's now almost 29 and in a rehab. Please do not be offended by the question. It's a very real possiblity. We owe it to our children to be honest and look at the possibility with open eyes.
I would also say that it's good that he has online friends. But, there is a caveat to that statement. Those online friends should *not* replace real life friends. I would not take away the internet either, but, I would limit it. He cannot become a hermit. He needs a real life with interaction with real people his own age. Try to get him involved in some activity he will enjoy; a sport; martial arts; music; whatever. That will get him involved with others who share the same interests, and friendships will grow from there.
There is a possibility that he may need more than just the school counseling. Once you speak with his counselor, you and that person can determine if outside counseling and/or medication is in order. But, please know that one thing ALL teens have in common is that they sleep -- A LOT! LOL! That, by itself, is nothing to worry about. Combined with the other issues you bring up, though, lead to concern. So, you are very right to bring it here and to show your concern. Continue to let him know that you are a resource for him; that he can come to you for support.
I wish you the best. Let us know how it goes. We care.
Peace!