What Causes Drowsiness All Through The Day?

My husband has been sleeping all day and can't stay awake for very long.. He said he feels drugged. I checked his blood pressure it was 140/78. I also checked his blood sugar, he had just ate and drank some orange juice, it was 114. I think his blood sugar was low before he at. He is sleeping again. He takes hydrocodone for chronic pain and said he did take a pain pill, hydrocodone 10/325. He has been on this for quit awhile and never had this happen.