Hello and thank you for your post on e health forum.
From the history and description it seems that your boyfriend has a infection in the brain (Meningitis or encephalitis)
Severe headache, fever with sweats, reduced sensorium, lethargy, excessive sleepiness are all signs of infection (viral or bacterial) in the brain.
Tests like a Lumbar puncture and CSF analysis, blood cultures, and treatment with specific antibiotics and supportive medications will help in resolution of the condition.
I hope this information here is helpful.