Underwater flips

Question
I was swimming the other day, (I have not gone swimming since last summer) and I decided to do a flip under water.  The first flip I did I plugged my nose with my fingers because I remember in the past doing flips that water would get into my noise and it was uncomfortable.

So then I attempted the flip without covering my nose and after doing the flip I felt a strong discomfort and pressure on my nose and inner eyes area.  What is this?  Why does this happen?  I ask my twin sister to do the same flip without covering her nose and she did not feel the discomfort.  

Answer
Vanessa--
This is just a result of the change in pressure from the top of the water to the depth you go under during the flip.
What happens is the water pressure creates pressure in your nose and the sinuses in your head(next to your nose and behind your eyes).  This causes the pain in those areas, it's possible you have a little sinus congestion that would contribute to that also.  Not all people have this problem, which would explain why your sister doesn't notice the pain.  
If you do the flip without holding your nose try blowing air out of your nose during the flip, this may also help.
Hope this answers your question.
George