He gave you IMMORTALITY, didn’t say nothin’ about remaining conscious!
And while suffocation due to CO2 accumulation doesn’t feel nice, HYPOXIA ON THE OTHER HAND FEELS AMAZING!
So:
step 1: shut off your oxygen feed and your suit heat
step 2: let the CO2 scrubbers do their job
step 3: breathe easy because you still have the ambient nitrogen mix component
pretty soon you’re gonna feel floaty, dizzy, and giddy - you’re gonna feel exhilarated, a real I CAN DO IT vibe - and then as a tingly and warm sensation engulfs your entire body, you will begin to feel HELLA sleepy.
then your immortal body will go into a state of persistent dormancy, preserved by the cold, purified by the radiation.
if you are EVER found (assuming you ever are… and if you aren’t, you won’t be in any condition to care!) and your rescuers expose you to an atmosphere your body can actually use, you will AWAKEN and be able to pick up however many days, weeks, months, years, decades, centuries, or millennia later, and resume living a life, even if it isn’t necessarily the one you once knew.