Is it dehydration? After exercising I felt I needed water so as I was gonna get the water my heart started beating fast, my vision became less visible, my hearing was less too and I couldn't breath right, feeling weak then I sat down and started to sweat

Sounds . Sounds like you might have had orthostatic hypotension of which the #1 cause is dehydration. What happens is that your blood pressure drops instead of increases when you change positions causing the symptoms you describe. I've attached a website with good information about orthostatic hypotension. Basically, make sure you are staying well-hydrated during exercise to avoid this in the future.