I should put this here in case anyone else needs to know about it: I move the cursor to an option on the game over screen, like 'Load' or 'Quit', then press escape to get back into the game. I tap F1 quite fast and more slowly press the escape key to bring up the escape menu. Go to Options and click or press escape to get out of that screen and you just come back to life with full health. You can use the same technique to open your inventory when you're dead. Just press your inventory key instead of escape when tapping F1. You can even teleport when you're dead by getting out a teleporter from your inventory, then tapping F1 and using E to activate it. It's not helpful if you're killed by a fish in Okasankaar because they just instakill you again before you can react, but it means you don't have to worry too much about dying elsewhere apart from the 7 or 8 seconds it takes to do this.