What would nausea without vomiting and excessive sleepiness indicate?

Not sure. These symptoms are not specific but if you have nausea and vomiting lasting more than a day or so you should see your doctor.
Gastritis & sleep ap. Get evaluated for sleep apnea as this may be the related to gastritis or reflux. Medication side effect, in adequate sleep, poor sleep hygiene, sleep interruption etc may be other causes. See sleep medicine doctor for further evaluation.