Is he on any meds at the moment, because I beleive some psychiatric medications, such as anti psychotics and anti depressants can have very bad adverse reactions on people with an ASD. I think this is because the ASD brain is wired slightly differently from your 'neurotypical' brain. So the drugs don't work in the same way. Think of it like electrical wiring, while most electrics work on an easily recognised set of wiring, some differ, although the currant still flows, just through slightly different wires. It's hard to explain.
His depression may or may not be related to his AS, but the two do go hand in hand sadly. It may be worth getting him checked out (if he would be willing) by a doctor for medical issues, things like thyroid function, low blood sugar, diabetes, food intolarance & epilepsy can cause altered mental states, sometimes very serious ones such as extreme depression, fatigue and appetite problems. Most of these things can be ruled out by a simple blood test.
Also digestive tract problems such as IBS are very common in people with an ASD, if you're effected by a problem in this area, it can cause a whole manner of knock on effects throughout the body if you're not metabolising nutrients propperly.
Also diet can have a prefound effect on people with ASDs, things like gluten, sugar & food additives & colours can worsen certain issues. What sort of things does he eat? It might be worth looking at his diet and seeing if any small changes might be of benefit, you could ask a doctor about this.
Does he drink alcohol or lots of caffeine or smoke, because none of those things will help someone who is depressed.
Obviously there will be many factors that contribute to how he is feeling at the moment. Tell him to go on the computer & just do some reading about aspergers, look for some personal stories from other aspies & print them off for him to read. Having AS is not miserable or horrible like some idiots would have you beleive.
Adult life for aspies can be particularly tough, those traits we might not have worried about so much as a child tend to be more noticable, if not to others then to ourselves. It's certainly not unusual for someone with AS to have low self esteem, I've accepted that as a part of my makeup sadly.
Some things you can't get rid of, it's like the birthmarks on my leg & neck, I know they're there, but they don't really bother me. It is ok to admit how you feel, there is certainly no shame in having AS or being depressed.
I would really have a think about trying to pursuade him to get some medical checks, just the fact he is in bed so much could indicate a physical problem of some sort. Try & pursuade him to go to the doctor (or change doctor if he's not happy with the one he has at the moment) and at least get some blood tests done.