TIA’s are episodes of decreased or lost consciousness due to decreased blood flow to a portion of the brain. Occurring underwater they can lead to drowning and/or arterial gas embolism.
Transient Ischemic Attacks are included in the list of ‘Neurological Absolute Contraindications’. These include:

• History of Seizure disorder
  Loss or change in the level of consciousness underwater is deadly.
• After head injury, disallow diving during that period of time that the diver is at risk for seizures.
  The diver should be completely free of changes in the level of sensorium, symptom free and be cleared by a neurologist as being free of seizure activity.
• Intracranial tumor or aneurysm
• History of TIA (transient ischemic attacks)or CVA (Cerebral vascular accidents)
• History of spinal cord injury, disease or surgery with residual sequelae. This includes a history of having had Type II neurological DCS with permanent neurological deficits.
• A history of unexplained syncopal episodes, whether cardiovascular or neurogenic.
• Peripheral neuropathies are disqualifying.
  Symptoms related to peripheral neuropathy mimic neurologic decompression sickness.

Bove, in ‘Diving Medicine’, states “Individuals with a history of transient ischemic attack (TIA) must undergo evaluation for cerebrovascular or cardiac disease before being considered for sport diving. Often a TIA is an indication of carotid disease, intracardiac thrombus, endocarditis, or valvular heart disease. These must be ruled out before consideration for diving”.

Diver’s Alert Network has the following to say about “stroke” in an article in the ‘Alert Diver’, May-June, 1999.
“Stroke, or loss of blood supply to the brain, causes damage to part of the brain, or bleeding from a blood vessel in the brain, which results in similar injury. Strokes come in all sizes and shapes, and the resulting disability depends on size and location of the event.”

Fitness & Diving:

• Most strokes occur in older people. The stroke itself identifies the person as one who has advanced arterial disease, thus a higher expectation of further stroke or heart attack.
• The extent of disability caused by the stroke (e.g., paralysis, vision loss) may determine fitness to dive.
• Vigorous exercise, lifting heavy weights and using the Valsalva method for ear-clearing when diving all increase arterial pressure in the head and may increase the likelihood of a recurrent hemorrhage.
• While diving in itself entails exposure to elevated partial pressures and elevated hydrostatic pressure, it does not cause stroke.
• There is certainly increased risk in diving for someone who has experienced a stroke. Exceptional circumstances may exist, such as cerebral hemorrhage in a young person in whom the faulty artery has been repaired with little persisting damage. This type of recovery may permit a return to diving, with small risk. Each instance, however, requires a case-by-case decision, made with the advice of the treating physician, family and diving partners. Consulting a neurologist familiar with diving medicine is also advisable.
• There is a similar concern for significant residual symptoms, as with post brain tumor surgery.”