I'm sorry you are having to deal with anorexia; it is such a difficult condition to treat.
As you probably know, this eating disorder can have severe effects on the heart. One of the most common--which you have--is an extremely low heart rate. Other very serious problems include a change in electrolytes, the ions that control the rate at which the cardiac cells fire. That's dangerous, as you can read here:
http://www.cardiacmatters.co.uk/how-anorexia-affects-heart.html
You do belong under the watchful care of a cardiologist at this point, to prolong your life.
Hi,
No, a heart rate of 19 bpm is not normal, not even during sleep. The immediate spike to above 200 bpm is abnormal as well, and very likely to be caused by some sort of arrhythmia.
What you should do:
Go to your doctor (preferrably today) and ask for a Holter monitor (24 hour continuous EKG). Explain to him or her what you have found. Of course, it may be possible that your heart rate monitor is wrong, but as long as there is a chance you may have an arrhythmia, you should get it examined.
The heart rate monitor are not good enough because the rhythm must be diagnosed, not just the heart rate.
See your doctor. A couple of conditions may be causing this, but it's not a good idea that you and I are sitting here speculating. You need a diagnosis.