Well as someone who has worked in nursing, it is not only the stressed that forget timing of their meds, but many seniors and or those on multiple meds have a hard time remembering when to take what, when they last took what, how it is supposed to be taken, or not taken with, and so much more.
Don't think the man committed suicide either. For one his cleaner was due to arrived and did so, she found him sleeping (and snoring), when she went in to change a light blub. Saw local NYC news last night, and the LE stated that while meds were found in the apartment, they were NOT scattered about, but in their bottles. So what you have is a man sleeping found nude in his bed with the covers messed about his body. Well lots of persons sleep in the all together, so that is not a big deal. Anyone who has every taken Xanax (I have before as pre-meds before two different operations), knows the right dose will clam you down, to much will totally knock you out. Indeed Xanax is routine given as pre-operative medication.
Now, sleeping medications, especially barbituates are GREATLY enhanced by Xanax. However IIRC, Mr. Ledger was taking Ambien (barbituate sleeping pills like Seconal nor Numbutal, are VERY had to get these days, and IIRC may be NLA in the United States), sleeping medications and Xanax are a dangerous combination. Again often given in combination with anti-anxiety drugs such as Xanax before major operations, but that is a dosage administered by a doctor or RN, and one is under a controlled setting. Also if one does not "wake" or goes in too deep, drugs can be given to reverse some of the effects to wake you up. Published reports state Mr. Ledger had complained about not being able to sleep recently, amoung other problems. If Xanax was taken in too strong a dose and or too close or with sleeping pills, there is a very real risk one may simply stop breathing, and or one's heart stop beating. You simply "go to sleep" and not wake up. Depressing the central neverous system either via drugs or booze is a very tricky thing, taken too low for too long and the system simply may stop, and without