Is it save to dive after taking flights?

Question

Let say,, last night I took a flight,, is it save to dive this afternoon?

I heard that we can get sick, because our body experiences extreme difference in height (after being at 40,000 feet then we dive to the ocean, below zero meter)

Answer 1

It's safe to dive after a flight, but not before.  Your blood will not absorb more dissolved gasses just because it was a little bit lower than it would be were you at sea level for a time before the dive.  It's decompression that is dangerous, not compression.  The only possible issue would be if you had a problem with your sinus cavities, then you might feel a squeeze & not be able to descend beyond a certain point, but it's not dangerous unless you force yourself past where you should go.  

The general rule is to wait 24 hours after a dive before you get on an airplane, to allow for complete off-gassing before negative pressure exposure.

Cabins are pressurized to about 3000' of atmospheric pressure.. regardless of the cruising altitude.