I have been taking nabumetone 1,500 , like you, for over a year. I do not know of any "sleepy" side effects.
Nabumetone is a non-steroidal anti-inflammatory drug (NSAID) of the arylalkanoic acid family (which includes diclofenac). Nabumetone has been developed by Beecham. It is available under numerous brand names, such as Relafen, Relifex and Gambaran.
It is used to treat pain or inflammation caused by arthritis. Nabumetone works by reducing the effects of hormones that cause pain and inflammation.
It has been shown to have a slightly lower risk of gastrointestinal side effects than most other non-selective NSAIDs.