Consequently if he is losing a lot of water via perspiration, then he is losing his fluid
volume, which will lower his
blood pressure, because low
volume means low pressure. If he is not experiencing heart palpitations, which can be caused by low potassium, then I would just suggest drinking gatorade while playing golf.
Also, is he on a low sodium diet? If so, then that would further put him at risk for hyponatermia. Is he on a diuretic?