What would pulse oximetry do? What is the patient's baseline/what is their underlying medical condition? If you're worried about decreased level of consciousness due to increased ICP, absolutely DO NOT lower the head of the bed.
I need more information than you've provided to properly answer this. I had a patient a few weeks ago (a child) who slept through my accessing her port-a-cath with no emla cream on. She didn't wake up at all when I jammed a needle into her chest, gave her chemotherapy and deaccessed her port. This is her baseline. When she wakes up, she is awake, alert, conversant and goes to school. So I would do nothing when she doesn't arouse even to painful stimuli because she is asleep and is just a heavy sleeper.
In general, you would check their breathing status. Basically, ABC's. The big thing with decreased LOC is how good they are breathing. Pulse ox would be a slightly correct answer if this was on a test and you had a limited number of choices to choice from, but as posted before, there isn't enough info to give a solid answer. If the pt had pneumonia, then breathing would definitely be the obvious. But, the specific assessment or intervention would depend on the situation or choice of answers.