We have a Svan highchair (don't buy one!) and ds2 bounces up and down when he's sitting in it.
always put him in, then do up his harness straps.
a few weeks ago, i put him in, didn't do the straps up, went and saw to ds1. then thought, silly mummy, do his straps so did them.
turned my back, a loud bang and the U-shaped bit of the seat had fallen on the floor, he then leant sideways and was hanging out of the chair, only the straps holding him from falling headfirst onto hard slate floor (don't get it if you're redoing your kitchen!)
i didn't want to upset either boy so calmly, went, la la la, oh dear ds2 you have fallen out of your chair, let's sit you up, la la la
redid all the screws/bolts before letting him get back in it and check them now for loosening.
ds1 never managed that trick!
oh, and my brother fell out of the car aged about 2. mum went round a roundabout, door opened, he fell out.
people behind were very kind and drove her, and all 3 of us to nearby doc who reassured her he was fine. his big duffle coat apparently cushioned his head. my mum still looks sick when she talks about it.
some of the ones on here are shocking, well done for admitting them though.
what was your near miss seriouscase?