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.