2 to 4 mg is the recommended dose for insomnia. If he had been on it for awhile he was probably taking the higher dose. For anxiety the recommended dose is 1 to 3 mg two to three times a day. Not to get to technical, but his toxicology showed he had a 200 ng/mL level of Ativan in his blood. A person between 50-240 ng/mL would pass a drug screening as being within therapeutic range.
Again, the drugs combined and the doses would make him drowsy and he might sleep for a long time. The medical examiner stated "these drugs did not contribute to the cause of death."