It's a Toshiba Satellite C55-B5356 (laptop). F3 itself just increases the brightness. Fn-F3, which is what I have to use for minecraft, is supposed to open a search bar in whatever program I'm using.
I updated to the new launcher and it's still happening, BUT I found the initial trigger. It always starts when I hit F3. I noticed after updating to windows 10 that all of the function keys seemed slow in minecraft and would stop working after a couple uses. I even had to change some controls because of it.
I think that the function keys are doing things that they aren't supposed to do while minecraft is open. I don't know if that's something that can be fixed by you guys or if I have to figure it out. Regardless, this is good info for anyone else that's having this problem.
This started happening to me after updating to windows 10. I tried to force the crash while it was happening, but I don't know if that would make any difference.
I also wanted to add that it usually happens very soon after I start playing. When it happens I have to either restart minecraft or wait a few minutes for it to start working again. Also, considering that this happens just as much in my superflat world as in any other, I don't think the ocean has anything to do with it.
Edit: Something else I noticed is that it only happens while strafing left or walking backwards. Walking backwards triggers a larger reaction in which the game pretty much freezes for a second. I thought this may be related to coordinates, but regardless of what direction I was facing it was always triggered by strafing left or walking backwards.
Disabling it didn't seem to do anything, but while messing with it I found out how to prevent it from happening. Remember how I said F3 was slow? If I just quickly press Fn-F3 and wait for the coordinates and stuff to pop up the bug/glitch happens, but if I keep Fn-F3 pressed until after all that stuff appears, it doesn't happen. I can even stop it after it's already started by holding Fn-F3 for a few seconds.