Hiya!
Its def your potassium/electrolite balance. When you purge (either vomit, or laxatives) you purge your body of the electrolites and potassium, and your heart needs those to function. Drinking gatoraid will only do so much...Its a really dangerous game purging, heart attacks and choking are scarily common.
I'm also 20, and been suffering since I was 13/14 from an eating disorder...And i'm finally making good steps from recovering, so if you ever want to talk or whatever...Pm me
<3 luisa xx