Walked to shop walking back went dizzy excessive sweating and seeing white spots hands shaking all of a sudden what could this be?

Dizzy: exersional dizziness is in common in young and there can CE several reasons.will need assessment by physician as a detailed history will be important to rule out anything sinister.

Low blood pressure: seems likely. Or you could be getting flu or something else. In either case, drink plenty of fluids, including something salty like broth, rest, and take it easy. If it doesn't get better, you need to be checked. Good luck!