Treadmill walking ?

My surgeon had me on treadmill on the day I got out of the hospital.  But I waited a few days because I was too tired and just moved around the house.  But when I did get on it I started at 1mph because my heart is at 45 and when I was on for 5 mins my heart rate jumped up to 188.  Did not seem right so I stopped.  I also go dizzy.