Blood pressure drop when exiting pool

Hi

Can anyone adivse me on how I can stop feeling faint when i exit the pool at end of swim going to T1.

I have only done one tri a tri and when i went to get out the pool, leapt out OK only to feel faint and had to sit in a heap for a minute or so before getting up and jog/walking out to T1.

It doesnot seem to happen when i just stop swimming and stand in water at shallow end, when doing my normal swimming.

I know it is something to do with blood pressure, not sure what to do.