My Husband Aged 82 But Very Healthy, Not Overweight And

My husband aged 82 but very healthy, not overweight and eating well, had a hip replacement 4 weeks ago. He takes Pradaxa (2 75 mg every morning. Is it normal to fall into quite a deep sleep several times each day. He is going for short walks and is quite active in between these deep slleps. Does the Pradaxa cause this or is it normal after this operation ?