My Husband Recently Received An Epidural Shot To His Neck

My husband recently received an epidural shot to his neck to help manage pain in his arms and shoulders. This usually invigorates him, but since the shot he has been falling asleep more than usual during the day. He is 68 years old and during the day he normally sleeps between 1 and 2 hours, through various cat naps. But lately he has been falling asleep, 1 to 2 hours every time he sits down, and has minimal energy.