Help my son has Hypertrophy obstructive cardiomyopthaty?

My son is 23 months and he has sereve hocm. he is a really bad sleeper at night time always waking crying and restless. do you know is this just a baby thing or is it too do with his heart. and is there anything we can give him to make him sleep a little longer at night. we are lucky to get 3 hours sleep