I just had a spell where my hearing became very dull, my heart beat fast, my eye sight was going in and out and i became very dizzy and had the urge to sit down and pass out. I experienced this a month or two ago at work during a hot and busy day and assumed i was over worked and dehydrated but it happened again not 10 minutes ago, and I havent been at work today, although I did just come back from the pool and took a shower. After sitting down and drinking something i felt a bit better but Why does this happen?