The reason is because, in a crowded dive boat, when it stop at a dive site on a choppy sea, alot of people will stay at the rear of the boat where they will gear up and get into the water. To gear up, normally they will put the tank on the floor to mount the BC. And if the sea is choppy, the boat will rock. And when someone lose balance and drop the tank. That's it if it falls on your feet. This was what happened to me. Gearing up for night dive. Then the boat suddenly rocked when i was transferring the tank to the floor, then i let go the hand holding the bottom of the tank to grab for support, then the tank fell on my toe. Luckily my the other hand still holding on to the valve area of the tank. If not the hold weight of the tank on my toe, i think my toe will be crashed flat. End up i had a cracked toe nail, and some cracked flesh around the nail. Painful you know, especially when you see the crew of the boat busy cleaning the area covering with all you blood foot print, while waiting for the other divers to returned from the night dive.
Normally i only feel abit headache and eyes tire and dry because i wear contact lens. Therefore i will drink lots of water and take a short nap and apply some eye drop for contact lens (must bring along). Drink lots of water before and after dive, as the compressed air you breath is very dry. This will add on to the un-comfortness. But if you have some "pinky" feeling around the joints, better consult your dive master of what to do. Oh yes, don't eat too much before or in between dives. But still must eat a bit, like one or 2 slices of bread to give you energy. Can go with peanut butter, basically because (according to one dive master) the vomitted peanut butter taste about the same as the "before-eaten" peanut butter, then you don't have that sour taste in your mouth. And if you know some people eat too much shortly before a dive, stay close to that person when diving, as he might vomit to feed fishes, and you can stay around to all the fishes in one go. Just joking. And for those who vomit on the boat into the sea, get ready your camera for the "merlion on the boat" shoot. Also joking.