why is my cheesecake sinking?!

Hot air expands. Cold air contracts. The problem is that you're overcooking the cheesecake, which causes the center to expand and push out the filling towards the edges before it sets up, then after it cools, the center contracts after the filling has set, so there's more filling around the edges than in the center. The solution is to use a springform pan wrapped in aluminum foil and submerged in a water bath, The water moderates the temperature of the cheesecake so that the center doesn't rise and expand, therefore it won't push out the filling and fall, since it won't contract after it sets. Overcooking cheesecake also causes it to be more dry, chalky, and more likely to crack. If you want the best control of the cooking temperature, buy an infrared thermometer (NSF food grade) so you can point and shoot the temp of the oven interior and the top of the pie during cooking. Oven thermostats are notoriously inaccurate. The temp will depend on the thickness. A deep cheesecake should be cooked at a lower temp for longer, then stopped at 150 deg. F. top surface temp, because it will continue to bake after removed from the oven. A thinner cheesecake can be be cooked at a higher temp for less time, then stopped closer to 160 deg. F. Most overcooked cheesecakes are allowed to rise above 170 deg. F. Cheesecake should also be cooled slowly, the thicker the slower. You can slow down the cooling by placing it under a larger glass bowl or pan. Throwing it directly into the fridge will greatly increase the chance of cracking.

My perfect cheesecakes are my research.

After reading several wrong answers, here is the correct one. You need to cool the cheesecake in the oven SLOWLY. Sometimes for 30 minutes to an hour. Shut the oven off 15 minutes before the end cooking time. Let in sit in the oven for an hour after you turn off the oven.

I think your over mixing it your putting to much air in the mix. so when it bakes it's rising like a souffle but since cream cheese so dence it sinks. try mixing it less with a paddle blade in stead of a whip. do over mix might crack. and cook it in a water bathhalf way up the pan.

use to bake 90 or so cheese cakes at costco every few days

I don't know the answer, but I just wanted to let you know that you're not the only one; it happens to me too!
The one trick I do know is for cracking, and that's to put a pan of water in the oven on the rack below. Not sure what to do about sinking. Sorry!

You hit the nail on the head! It's the electromagnetic waves generated by the high voltage heating element in the oven. It's similar to what happens to people living under power lines. Get a gas oven.