The Pope knows the value of the correct dosage There are, however, a couple of useful rules of thumb. First, obviously, drugs should alleviate the symptoms for which they are prescribed. When, for example, the aches and pains of an arthritic knee persist despite taking anti-inflammatories, it is only sensible to consider taking something stronger. The disturbing feelings of "alarm and unease" when climbing a ladder or in a crowded shop, as recently described by a reader since recovering from a severe attack of vertigo during the Plymouth-to-Santander ferry crossing, has prompted a most persuasive explanation from Dr Peter West, specialist in audiovestibular medicine at Queen Alexandra Hospital, Portsmouth. The phenomenon of balance, he said, depends on the subtle interaction of three factors: visual cues, the balance mechanism in the ear and "proprioception" - the appreciation, moment by moment, of the position and degree of flexion and extension of the limbs. An acute attack of vertigo following, for example, a stormy ferry crossing can cause the brain to become overdependent on the visual cues. These can, however, be misleading in excessively "busy" visual environments such as crowded shops, setting off a vertiginous situation that, exacerbated by a phobic or panic reaction, can become overwhelming. This pattern of symptoms is apparently not unusual, warranting a thorough assessment by a specialist skilled in this field who will be able to advise an appropriately adapted series of exercises. "It is always remarkable," he writes, "how much patients improve once they have a proper understanding of the nature of this problem." This week's medical query comes courtesy of Mrs E S from Hertfordshire, who keeps fit with a brisk half hour walk every day. She reports that when setting out she has variously a "jelly sensation" or "woolly feeling" in both legs which gradually disappears after she has been going for 10 minutes. She wonders whether anyone else has had a similar experience or what the explanation might be. All suggestions, as ever, gratefully received. Email medical questions confidentially to drjames@telegraph.co.uk. Dr James LeFanu will host his final online health clinic of the year this Friday, Dec 20, at telegraph.co.uk/health. The clinic will then return on Friday, January 10, 2014