Been there, a few times. The worst was 3 years ago, I was mowing pastures with my 7710 and 15 ft' batwing. Rear wheel got caught like that one. It just worked out though that a neighbor that runs a bulldozer, had his fairly close and in between jobs so he came and pulled it out. The location of it was down at the bottom of a hill and had the batwing not been hooked it it would have likely turned over getting it out. When it happened it didn't shake me up much until I saw it after getting off the tractor. Getting back on and guiding it while the bulldozer pulled me out was pretty nerve wracking.
We have a lot of sinkholes here, and we are finding new ones the hard way like that more often than I want to think. Even have had one drop out in the front yard about 6-7 diameter, and probably a good 5 ft deep. We have a lot of limestone and underground springs around.