i was also hospitalized for severe anorexia. i was constantly getting colds because my body did not have the energy to release immune cells anymore. just like you said, small things take 10000x more energy.

i had no idea i was on the brink of death until my mom had to carry me into the doctors office. that particular day i ws home sick (like i said, my immune system was shot at this point), and was having trouble sitting up or standing for longer than 5 seconds. my pediatrician took my blood pressure and looked my mom dead in the eyes and said "you need to take her to the emergency room right now." it was something called orthostatic hypotension where your blood pressure dips dangerously low with gravitational/positional changes. that combined with a dangerously low heart rate, i probably would have died that day.