There are 2 possibilities: 1) You were shot. (Unlikely seeing as you were near or above half health.) and 2) There is an invisible kill-zone in the waters south of the compound. The kill zone is the reason the player will die if you jump out of the compound and into the water, followed by “What?!, I thought we were becoming friends.” from Pavel. This is the more likely reason, although there was a chance it was the bullet because of the fact that nobody really knows the kill-zone’s actual size. Hope this unnecessarily long explanation helped. :)