So I'm driving down the freeway and suddenly (this may be a coincidence) my speedometer goes crazy, drops to zero, boing boings around for a second then stabilizes, and at the same time the a/c keeps blowing, but stops blowing cold air and is just plain old hot air. Speedometer is fine now but a/c is still not cooling. Did something come loose? Any ideas? Thank you!

 

I'm just going to through something out there to get you started because I have never heard of this before, start with having the battery and alternator tested.
I had a car that the alternator went bad and would not charge the battery but was putting out enough volts to not set off the battery warning light and nothing worked, no power windows, no stereo, no a/c, nothing except the engine.

 

AC compressor clutch is an electrical device, could have had a momentary electrical fault (short to ground) that impacted other displays before the fuse blew for the clutch (if it blew). That might be an area to start on, under hood fuse box, etc. And same as Spike says, alternator can be so low that battery drops below range that everything operates at, eventually runs all the way down and fuel pump quits.

 

Try putting in a new battery. bad batteries cause that issue alot more then alternators. Never seen the ac completely stop working but start with the battery and then check to see if the clutch is actually moving when you turn on the ac.

 

Did you check the a/c fuse, have you looked to see if the a/c clutch is engaging?