I did that once too - fell asleep. It was the end of a long day in the saddle and I was only a couple of km from home. I have no memory of the event but a mate following me said my head drooped down and I kind of slumped on the bike (Honda 750 K1) and made no attempt to negotiate a roundabout. I woke up in hospital with a ruptured kidney. Apparently I hit my back on some street furniture as I slid/tumbled down the road. My mate said I sat up and was talking for a couple of minutes before passing out, but I have no memory of that either. Someone must have called an ambulance from a nearby phone box (before the days of mobile phones). They kept me in hospital for 10 days until my kidney healed enough so there was no blood in my urine. Even so, I figured I was better off than the young guy in the bed next to me. His little brother had accidentally shot him in the wedding tackle with a .22 rifle. The bullet went through his penis, a testicle and ended up in his inner thigh. They patched up his dick and removed the perforated knacker. That's not a good way to get circumcised.
In more than 50 years of riding, I've had too many unplanned get-offs to remember. The worst were hitting other vehicles (their fault on every occasion). I've twice had cars travelling in the opposite direction turn across my lane and wipe me out.
The first time a car turned in front of me, I was on a 1967 Yamaha YDS5E (250cc twin 2-stroke). I was 17 years old. It was my first bike and I'd only just got my licence. The car driver suddenly turned straight across in front of me with no indication that she was turning. I hit the front of her car at 60 kph and was catapulted over the top of it. The brain must speed up at such times of mortal peril because I remember it all like it was happening in slow motion. I flew through the air like superman and landed in a broken heap on the road. Some passers-by looked after me and called the ambulance. They were well-intentioned but did everything wrong. They rolled me over, dragged me off the road and someone tried to take my helmet off without undoing the chin strap. It felt like he was trying to yank my head off. Luckily I didn't have a spinal injury, but they weren't to know that at the time. Some kind lady put a blanket over me to keep me warm, but it was a stinking hot day and I was lying in the sun with my black leather jacket zipped up. I kept trying to push the blanket away but she kept pulling it up around my neck and tucking it under me. I reckon I was lucky not to get heat stroke. I had a smashed knee, broken arm, concussion, and lost some skin off my hip and lower leg (was wearing jeans that got shredded - couldn't afford leather pants in those days). The pocket of my jeans was ripped open and my wallet fell out as they dragged me onto the footpath. It was returned to me while I was being loaded into the ambulance, but all the cash was gone. It was only about $50, but that was a lot of money to a teenager in 1968. It has to be a special kind of low life that steals money from a 17 year old kid injured in a road crash. The driver of the other car never got out of her vehicle. A police officer who attended the scene later told me that she was very upset, and she thought she'd killed me (probably because she saw someone put a blanket over me). She didn't want to look at a dead body. She was obviously quite traumatised by the event.
The other time a car turned in front of me was several years later and I was on my long-suffering Honda 750 K1 (that bike got crashed several times, not only by me). It was at an intersection in the city late at night. I had a green light, he had a red arrow, but it didn't stop him turning in front of me. I was only travelling at about 50kph and almost managed to avoid him, but not quite. Just a few scrapes and bruises that time. He took off but several pedestrians standing at the corner got his number, so the cops picked him up within minutes. He was a young bloke with a car full of his pissed mates. Apparently he'd been hooning around, doing burnouts and stuff just before he hit me. He also had about 3 times the legal limit of alcohol in his system. Police threw the book at him for a whole bunch of offences. Surprisingly, he only got a token fine and no points off his licence. But he did at least get a stern talking to by the magistrate. I found out some time later that his dad was a barrister and a mate of the magistrate.
I had a Kawasaki 900 Z1B that I chucked down the road a couple of times without serious injury. Both times due to oil/diesel spills on the road.
The only times I ever came off due to excessive speed in bends were on the race track. Only low-sides. Never had a high-side thankfully.