He said that when you have an eating disorder/ are malnourished, most of your blood goes to your core to keep your temperature up- that is one reason why often people will have cold or blue limbs. When you take a hot shower, you shock your extremities with extreme temperatures, and your blood is forced to rush away from your core to your limbs. This puts extra stress on your heart, and because most disordered patients already have a weak heart muscle, the heart has to pump abnormally fast because it isn't strong enough to push the blood out quick enough. This is why a lot of people feel their heart race or get dizzy, and he said many of his patients actually pass out in the shower if it is too hot.
Have you had this issue? Discuss. :)