For a variety of reasons, but "running on edge" is in this case defined as "working too hard without enough sleep" in the most general case. Going to Six Flags last Thursday after only about two hours of sleep the prevous night I think is what finally pushed me into a state of exhaustion.
I've spent much of the intervening time asleep, and I don't even have anything resembling a sleep "schedule" now. I just woke up about half an hour ago- 8:30 PM- from going to bed at 8:45 AM; I'd woken up before then at 11:45 PM from going to bed at 5:45 PM earlier. Eleven consecutive hours are the worst I've done yet this time- it's not the fifty something consecutive hours I slept when I caught the flu a few years back- but the total is somewhere around 15 hours asleep in a 24-hour period, and that's not entirely cool.
But it's obvious what it is; my father has been known to do the same thing in certain situations. It's exhaustion, born of months of sleep deprivation and then one event of major fatigue. My father had the same from being hired as a computer consultant and working 100-hour weeks with nearly weekly airplane trips on-site to Texas. Profitible, but exhausting- it's like he wasn't there at all for the worst two years of that work, because when he wasn't in Texas, he was either working or comatose, and frequently the latter.
I do need the rest. I have been running on edge for a month and a half, and it's finally decaying. I just need to get this resolved in time to finish my lab assignment and take my final exam on Wednesday...