Headache for 20 hours now, fatigue and malaise feeling. warning sign of impending stroke? should i be scared?

Headache: If you've had a headache for such a long time you need to see a doctor ASAP. You need to have your blood pressure checked and may need a CT scan or MRI of the brain. With your age I would be more suspicious or a migraine or an aneurism than a stroke. Either way you need medication attention

More likely viral: In someone your age without risk factors for stroke a virus or other etiology is more likely. If you are at increased risk of stroke, seek medical care for a complete evaluation. If not, take your temperature and if low grade is likely a virus, but if it persists or worsens see a primary care physician.