Possible diagnoses could include:
More common in older patients. Does not usually cause fluctuating symptoms like yours, unless it is caused by vasculitis (inflamed blood vessels). However, vasculitis would also cause other symptoms such as lethargy, muscle aches, jaw ache, and is uncommon under the age of 50.
2. Infection (eg encephalitis)
Can occur as part of a generalised viral illness (eg flu, or Lyme disease) - but again, this would give you other symptoms such as headache or neck ache.
3. Inflammatory neurological problems. More common in temperate and colder climates (not in the tropics).
3. Latent strabismus
(misalignment of the eyes) which you are able to control most of the time, but which you lose control over when tired or stressed. This could cause the symptoms you describe but would likely give you double-vision.
If you are getting double vision, I would suggest an ophthalmologist
for a squint assessment. If there is not double vision, perhaps a neurologist is more appropriate.
I hope this is helpful. If so, kindly click 'accept.' Best wishes.