Dizziness that occurs while diving can be dangerous. Some divers felt they were going to blackout, while others had brief periods of disorientation. Either of these consequences can result in an accident and an accident underwater may be fatal.
There are many causes of dizziness, but in diving, a few need to receive special consideration:
Hyperventilation – A trace of subconscious anxiety in a new diver or a minor mishap underwater can result in excitement and hyperventilation. The worst case I witnessed was a new diver using an entire 80 cubic foot, 3,000 psi tank of air in 10 minutes at 30 feet. The hyperventilating diver may be unaware of his/ her condition, but the profuse cloud of bubbles rising from his/her second stage gives him/her away. By breathing too much, the diver lowers the CO2 in the blood and upsets the chemical balance of the body. Dizziness, shortness of breath, numbness in the fingers and toes and spasms of the hands and feet can occur from hyperventilation. Severe hyperventilation can cause a blackout. Sometimes the amount is not enough to be obvious to another diver, but still enough to produce dizziness.
Preventing hyperventilation depends on awareness. If you consume air at a rapid rate, are constantly short of breath or feel some anxiety during the dive, you may be hyperventilating. Consciously slowing your breathing rate, even if you feel short of breath, usually solves the problem. The new diver with hyperventilation problems often can overcome them by diving with an experienced and confident partner who can provide advice during the first few dives.
Middle Ear Imbalance
The ears are not used just for hearing. Closely connected to our hearing apparatus are the organs responsible for balance. Called the semicircular canals, they keep us oriented relative to gravity. The balance organs can be stimulated by several events encountered in diving. On ascent, when the middle ear is decompressing, pressures can be different in the two middle ears. This situation is called alternobaric vertigo. Both dizziness and vertigo, a sense of spinning, can occur when the semicircular canals on the two sides are stimulated unevenly. The sensation of dizziness occurs on ascent. It can be stopped by slowing down and making sure both ears are decompressing properly. If you had problems clearing your ears on descent, you will be more prone to this on ascent.
Uneven cold stimulation to the ears will produce the same sensation. If you are diving in cold water and lift one side of your hood, cold water will reach one ear while the other remains warm. The difference in temperature stimulates the balance mechanism unevenly and results in dizziness or vertigo. You can avoid this by keeping both ears at the same temperature when diving in cold water. This is best done with a wetsuit hood. Be prepared for a dizzy spell if you lift one side of the hood.
Abnormal Heart Rhythms
Although rare, when no other cause is evident, we must consider the possibility that an abnormal cardiac rhythm is causing dizziness. If the heart beats too rapidly (tachycardia) its pumping function is diminished and dizziness will occur. A rapid heartbeat can occur from too much stimulation. Caffeine and adrenaline-like drugs present in decongestants can overstimulate the heart. A severe slowing of the heart beat (bradycardia) also produces dizziness. There are some people who develop very slow heart beats when immersed in water. This is a rare condition and would cause blackouts at the beginning of a dive.
Excessively high or low blood pressure can cause dizziness. People who take blood pressure medicine may experience dizziness from low blood pressure. Consultation with your doctor and changes in drug dose are necessary in this case.
You must consult a physician for other causes of dizziness. Because of the numerous possibilities, a thorough evaluation is needed. The most common cause of dizziness on ascent in a healthy diver is alternobaric vertigo. The effect is usually brief and with more experience, methods of decompressing the middle ear on ascent can be developed.