First, please understand that it is impossible to correctly say what happened to you without more examination. There are always many possible answers. We can only guess and you cannot trust any of this. If you have a problem that worries you, you must see a doctor.
Although you say drinking water makes you feel better, it can also be that the time delay it takes to drink the water is helping you feel better. This can be an important difference because it makes us think about other problems which can cause dizziness but are not directly related to drinking water.
If the "dizziness" feels like spinning or you cannot balance or walk straight, then you might have a problem with your ears. It may be caused by not equalizing correctly or water is getting into your ears. Be sure that you are equalizing properly. If this doesn't help, then you should be examined by a doctor to check if something is wrong with your ears.
If the "dizziness" feels more like you're going to faint or vomit, this problem might be very serious. This can be caused by a problem with your heart or lungs or a problem with your blood vessels so that not enough blood or oxygen is reaching your brain. Make sure you breathe normally while diving. As soon as you can, you must be examined by a doctor to see if your heart and lungs are ok to work hard for diving. After that, your health should be regularly checked by a doctor.
If the doctor says your health is good, then another common reason to sometimes feel bad and faint is dehydration. Scuba diving makes you lose lots of water from swimming and breathing cold, dry air and being submerged in water. Eating a big meal before diving can also make your stomach use more water. Before diving, you should drink enough water to make your urine to come out colorless or almost colorless. After diving, you must also drink to replace the water lost.