SAT Divers breath Heliox which replaces the Nitrogen content with Helium. One of the effects experienced is an increase in the pitch of the voice and sounding like 'Donald Duck'
Radio transmissions can't propagate underwater. Submarines must float an antenna to the surface to transmit any radio messages. The diving bell deployed no such equipment, yet the divers communicated with two ships.
The diving bell is always at pressure so its not actually possible for the young guy to get an embolism in his cavity while inside.
At the beginning of the movie you see Jones and Hurst calling their loved ones using cell phones. It is highly unlikely that they would have any cell phone reception capabilities in the middle of the Indian Ocean.
Young Cole's character has extreme pain from a dental embolism as the bell falls, as pressure increases. But, it's backwards, pressure in a dental filling occurs on decreasing pressures.
The lighting inside the pod flickers extremely when an oxygen tank malfunctions. The malfunctioning tank should not cause this electrical disturbance. However it makes good dramatic effect.
The coordinates given (19.14E 71.33S) is nearly halfway from Madagascar to Indonesia, and around 4km deep.
From the moment they reached the pipeline and saw the position mark they new their relative position that is good enough for quick rescue. It was written on the map they where looking to. When reached the second position (emergency tank) with full length of the umbilical they knew the distance. With simple math they could get the coordinates with several meter precision. But yet when asked on radio they chosen to say they don't know where they are.