Occasionally, a diver may experience dizziness while diving. Some experience dizziness while on the bottom, others while ascending; few complain about feeling dizzy during descent. Dizziness can represent a variety of problems. It can describe a feeling of lightheadedness or a sensation of spinning (vertigo). Lightheadedness is usually associated with conditions that lower blood pressure. If blood pressure falls low enough, the blood flow (and thus oxygen) supplied to the brain is reduced and dizziness occurs.
Other causes of dizziness include situations where inadequate oxygen is provided to the brain even though blood pressure is normal. Breathing oxygen-poor gas mixtures or carbon monoxide or not breathing at all can cause dizziness. An inadequate glucose (sugar) supply to the brain deprives the brain of fuel and will also cause dizziness. Vertigo is caused by abnormal stimulation of the balance mechanism in the inner ear.
Dizziness that occurs while diving can be dangerous. When it is caused by a lack of oxygen or blood flow to the brain, a diver may blackout or have brief periods of disorientation. Either of these consequences can result in an accident and a fatality is likely. There are many causes of dizziness but, in diving, a few need special consideration.
HYPERVENTILATION: A trace of subconscious anxiety in a new diver or a minor mishap underwater can result in excitement and hyperventilation. The hyperventilating diver may be unaware of his or her condition but the profuse cloud of bubbles rising from the regulator is a telltale sign. 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 hyperventilation is not obvious to another diver but is 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 lowering the rate and depth of breathing, 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 only used for hearing. Closely connected to our hearing apparatus are the organs responsible for balance. These organs, called the semicircular canals, 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 is called alternobaric vertigo. Both dizziness and vertigo can occur when the semicircular canals on the two sides are stimulated unevenly. It can be stopped by slowing your ascent and assuring that both ears are equalizing properly. If you had problems clearing your ears on descent, you will be more prone to this effect on ascent.
Uneven cold stimulation to the ears will produce the same sensation of vertigo. 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 the problem by taking care to keep both ears at the same temperature when diving in cold water. This is best done with a wetsuit hood. Be prepared for vertigo if you lift one side of the hood. Occasionally, a viral infection involves the balance mechanism. The infection (labrynthitis) causes severe vertigo and vomiting, as though you had motion sickness. When this occurs, the only recourse is to go to bed and keep your head absolutely motionless. Even the slightest motion can cause vertigo and nausea. This usually lasts a few days.
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, blood pressure will fall 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 heartbeat (brady-cardia) also produces dizziness. There are some people who develop very slow heartbeats when immersed in water. This is rare and would cause a blackout at the beginning of a dive.
OTHER CAUSES: 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.
For other causes of dizziness, you must seek medical consultation. Identifying the cause among the numerous possibilities requires a thorough evaluation. The most common cause of dizziness on ascent in a healthy diver is alternobaric vertigo. The effect is usually brief and, with more diving experience, methods of equalizing the middle ear on ascent can be developed to avoid the problem.