I feel high, unable to focus, headache, n nausea when I drank coffee. Why?

Caffeine effect. You are drinking too much. Caffeine generally produces sharpness and clarity of thought, but if you drink enough you can really lose all that. You may be very sensitive to caffeine.
Metabolic effect? Caffeine is a stimulant, has other metabolic effects. It acts as a diuretic & causes a urinary excretion of calcium & magnesium. In some people this mineral wasting can lead to excessive systemic alkalinity (oh-). High oh- can lead to a spaced out feeling, or drowsiness. Also high oh- can stimulate your parasympathetic nervous system (pns). Pns excess can cause h/a and nausea www.Mdwellnessmd.Com.