I never had that happen to me before. My best guess is that the server lost track of your health stats or it is just an (undiscovered?) glitch with the slot machines in SA:MP. I rarely play the slots, though, so I cannot be sure.
-Unless... someone shot you while you were in the middle of playing the slot and the the game couldn't show you the "wasted" screen until you exited the slot minigame so the screen just showed red. This could only have happened if there were others online while you were playing, but I think it would explain the red screen, delayed death, and the game taking it as a suicide.