BMR/ 24 Hour Heart Rate Monitor

I went on a 2 hour, super strenuous hike Saturday and according to my Polar F7, which I enjoy, I burned over 1100 calories in that 2 hours. I didn't think that was crazy because it was a a serious hike (and I am 5'7" 215 lb, 34 y/o female with a large frame, muscular build, plenty of weight to lose). So I got to wondering just what my BMR is and how many calories I burn just being me in an average day.
So I put on my heart rate monitor yesterday at 8:12am after my shower. I then ate, painted a bit in my bedroom (it's under construction) but this was not strenuous, my HR never got above 114 (I checked, I was curious). Then I went to work. At work I walk around frequently, but very casually. I did take the girls to gym (I work in a juvenile detention center) and I did 2 jumping jacks with the girls (they knew I was wearing my HRM and they wanted to know how high it would get) so my HR got up to 132 briefly, but that was the max for the whole period. After work I came home, petted the dog, and went to bed.
I wore the monitor for 23 hrs and 58 minutes. It says I burned 3850 calories just being me for the day. There is no way I eat nearly that many calories (I have not recorded my calories here lately, but I have in the past and most days I'm in the 1700-1900 range).
I am thoroughly confused.
I know that my Polar F7 is accurate as far as my HR, I've checked it manually. and the watch does allow me to program in my age, sex, height, and weight.
Is the computer program used to guesstimate calorie burn really that far off? And if it is, how on earth can I ever actually figure out how many calories I'm actually burning??

Has anyone else ever worn their monitor for a whole 24 hours? That's what I'm wondering... anyone else had a similar experience?

Oh, also, before I went to bed, I checked the calorie burn so far... I was at just over 3100 before I went to bed. Which means I burned 700 calories sleeping for 7 hours?? Is that right? 100 calories an hour to sleep peacefully???