Combat log
Double check that your “combat options” have all sources of incoming damage listed.
Besides that, can you add some details to where you are/what you’re doing when you are “one shot”? I run a glassy mesmer in WvW and I can’t remember the last time I was one-shot by anything, even fighting really stellar warrior, thief, or ele. I suspect something more complicated is going on than a single hit taking all your health.
John Smith: “you should kill monsters, because killing monsters is awesome.”