What should you do if you suddenly feel ill and/or develop a headache during a scuba dive?

You should come back immediately, but not fast, to the surface and get fresh air.

Explanation:

    Scuba diving is the practice of diving that consists of partial or total submersion in the water, using for this purpose, a self-contained breathing apparatus, also known as diving equipment.  

  During scuba dive, a lot of problems can happen because of the depth and compression of the air, so in any case of feeling ill, you need to come back to surface.    

  In scuba diving, the diver is assisted by equipment that he carries with him and allows him to breathe underwater. Although physical activity is healthy even for those with a basic respiratory disease, diving is a sport that requires redoubled care. When the individual dives, the gases in the diving cylinder dissolve in the blood because of pressure greater than atmospheric pressure. The phenomenon becomes more intense depending on the depth and gases used. Compressed air gas is the most common used in recreational diving. At greater depths, gas mixtures such as helium and oxygen or helium, oxygen and nitrogen are used.

  The main problem is not the dive itself, but the risk of decompression when the individual rises too quickly to the surface. Residual nitrogen is the nitrogen remaining in the body after a dive, whose delay time to be eliminated depends on the dive time and depth reached. If the elimination of residual nitrogen is deficient (due to health or external factors such as a very rapid climb), nitrogen bubbles that cannot be eliminated from the human body can become trapped in tissues or in the bloodstream. This occurrence is called decompression sickness. When this occurs, gas bubbles form in the circulation that can cause myocardial infarction (heart attack) or stroke (stroke).

hmmm

true, i think.

i checked and it seems the answer is, true.

9, 5, 10000000 ( that is supposed to be a ten for the last one)