That's it, the disciples sleep a lot. And they sleep at important moments. In last Sunday's Gospel, St. Luke's account of the Transfiguration (Lk. 9:28-36), St. Luke tells us that they fell asleep and only began to wake up as the Transfiguration was almost finished. In the account of the Agony in the Garden (Lk. 22:39-46) and in St. Mark and St Matthew's versions as well, we find the disciples described as having fallen asleep. If it happens to them then it must to us as well; what does it mean?
Remember being in graduate school at Columbia and after a full day of work, riving to Morningside Heights to take two courses. More than once I remember starting to doze and snapping back to life, afraid that I may have started to snore -- didn't happen, thank God. That's the sleep of being tired. St. Luke's gloss on the disciples in the garden is that they were sleeping from "grief". Overwhelmed by this feeling they fled the conscious world. I think it's a metaphor for what I would call "inattention". They weren't paying attention to what was really going on; they didn't realize what was happening. How could they have missed it? Other things cloud the mind, and Jesus seems not to be the focus of their attention. If it can happen to the disciples who were physically in His presence how much the more likely it will happen to us?