Very rarely. When I do, usually I trip over something.
I’m not the most graceful, I have amblyopia (hence somewhat poor depth perception), and often bump into things and slip and trip, but I almost never go down. I can’t even remember the last time. I am a very cautious person, always have been, very rarely got hurt even as a child, so I think that’s most of it. I’m also pretty athletic and have better balance than the average person due to yoga.
I know some chronic ‘fallers’ - my mom (who used to fall down our stairs a couple times per year, I hope she’s not still dong this because she’s getting old!), a long-time friend of mine who falls down almost every time I hang out with her to our mutual amusement, a co-worker, and my boyfriend. The co-worker (an athletic woman, and otherwise very graceful!) falls constantly and often really hurts herself, last week she fell full-length leaving her house (no rain or ice involved) and smashed her chin on a concrete step, she still has a scab and she’s lucky she didn’t break her teeth! Thankfully BF never gets hurt - he usually slips, his feet go up in the air, and he falls on his butt - but it’s great entertainment.
If I had a superpower, that power would be Not Falling Down. I’ve been known to hit a patch of slippery ice, proceed forward for 3 feet, then put my other foot down and continue as if nothing happened. It’s really weird.
ETA : Probably back in High School (so ca. 1997); I know I fell three times in the same year, due to my damaged right ankle.
I did that once in the 70s. It was quite a long tumble – I passed a fellow on the way down.
The good thing was that it was during a cross-country foot race (the Eastern Canadian Championships held concurrently with the Ontario Championships). I ended up coming in one place better (17th) than the fellow whom I fell past, and that one place landed our team the Ontario gold above his team. One small slip for a man; one giant tumble for . . . 
I ripped a ligament (or tendon? Not even sure anymore… this was 30-some years ago) in my right ankle in a bizarre astronomy accident. Despite having surgery to re-attach it, I still have very limited lateral stability in that ankle. This destroyed my pro-basketball career, obviously.
Spending the majority of the last couple of years of high school/first couple of years of college in and out of a cast taught me this: when the ankle gives, DO NOT try to recover! Just fall down. If I try to recover, I end up in a cast. If I fall down, maybe no one sees. 
So I fall down a few times a year if I’m not really careful.
I have pretty crappy depth perception, balance, and proprioception, so I tend to trip/stumble over stuff ALL. THE. TIME. I rarely hit the ground,though, so I don’t know how you’d class that.
I don’t fall down regularly. I do sometimes fall down, but those instances are rare and require special circumstances. I do a lot of work on ladders and man lifts if falling down randomly was an issue I’d be pretty dead by now.
I suck on slick surfaces due to a knee injury/a difference in length of my femurs.
I am clumsy, and I have a terraced house built 1895 with steep, narrow stairs. I have big feet, and apparently Victorians…did not. So the stair riser is only maybe 3/4 of the length of my foot deep.
Add to this that my house did not originally have indoor plumbing, so the bathroom is tacked on to the back of the house (every Australian is now nodding and able to picture this.) To go to the loo in the night I have to get up, go downstairs (oh, and they twist at the bottom by 90 degrees), go down two more steps into the kitchen, one of which used to be the backdoor step so it’s worn down and made of stone, then go down through what used to be the outdoor kitchen fireplace four more steep, narrow steps and then to the loo.
I fall down often. I have not yet wiped it at the top of the stairs (our poor doggie did and tore his cruciate, poor bubba will have surgery soon). I have wiped it usually either:
- Where the stairs make the twist, because I am sleepy and miss it
- When I forget there’s just one more step and I miss it (not so much anymore, there are 14 steps and I have learned to sleep-count them
- If it’s humid, on the stone kitchen step
- At the top of the stairs down to the bathroom - this is most usual, and doesn’t require sleepyness, just a total misstep of any kind and you slide down it like a kid at the park.
Lights on or off doesn’t seem to matter. My house is trying to kill me - and just me (and my poor doggie, apparently) because no other member of the family has ever stacked it. My husband, my kid (who lives up the other side of the house at the top of his own steep stairs), the other dog and all three cats are fine with it.
Gah. I am generally covered in bruises.