problems with running on mac

hey guys. my minecraft runs fine on my mac with no lag or anything but after 5-20 mins minecraft freezes my whole computer and I have to turn it off with the button as I can't move or do anything.

Anyone have a fix for this please?

 

More information please, does your minecraft screen have an error message when this happens? Just a random suggestion that might work, but it might not since I do not have enough info, like does your screen go black or w/e but try doing Control+alt+delete to open task manager, and set your minecraft to low priority.