So, I had just come out of Fort Bannister having killed all the Talon Mercs. I met some Brotherhood members outside and decided, just for fun, to kill them. Awhile into the battle, I died. I assumed I had forgotten to pay attention to my healthbar and reloaded to try again. Soon I died again. Since I ,being lvl 30 with Tb-51 and a plasma rifle, it is no easy task to kill me, I became suspicious. The next time I kept a close eye on my HP and found that it has only half drained when I suddenly died. There was no explosion or message, just a collapse. Two more tries yielded the same result. The sixth time, I did not get into a battle and simply left the Knights and Paladins alone. Since then, I have had no random deaths. Any ideas on what could have caused the problem?

Check your radiation levels? If it gets to 1000 then you automatically die. If your radiation levels are high then take some Rad-away. This happened to me when I first got the game. I would jump into the water and automatically die.

No, my radiation was low. I didn't even have Minor Radiation Sickness.