These drugs have side effects. Frankly, anyone taking this stuff should be aware that if it makes you drowsy or worse, that you should not be standing watch by yourself.

There are medical studies that indicate that taking Dimenhydrinate and diving is hazardous to some degree. I have no further information about any of the other drugs, but I would be especially careful of any Scopolamine products, and diving.
 

This link at medscape.com has a paper on the Hazards of  Diving