We all have our off days. Winston Churchill, for example, had the famous "black dog" of his depression that followed him around from time to time, and Admiral Beaufort, originator of the Scale of Wind Force, had his "blue devils" - similar troubles of a different hue.
Antonio in The Merchant of Venice was also familiar with the feeling. "In sooth I know not why I am so sad," he tells us, and then goes on to deplore the mystery origins of his malaise: "But how I caught it, found it, came by it, what stuff 'tis made of, whereof it is born, I am to learn."
Nowadays, some such symptoms are attributed to SAD, the acronym for Seasonal Affective Disorder. SAD is identified as a form of chronic depression - a melancholy allegedly associated with lack of sunlight during the winter months. The link, apparently, is the tiny pineal gland at the centre of the brain, which, inter alia, produces a hormone known as melatonin. The gland is triggered into action by light, whose presence or absence it detects by means of signals from the eye; darkness prompts it to secrete "the Dracula hormone", as some people call melatonin, and light signals it to stop. And an excess of melatonin, some allege, predisposes people to depression. Too much of it, it seems, and we just cannot cope with winter any more. The latest posthumously identified victim of SAD is the Finnish musician Jean Sibelius, composer of Finlandia and many other works. Although a charming person when in the public eye, Sibelius appears to have been what some might mildly call a difficult man in private life. Analysis of his behaviour, however, has suggested recently to experts in this field that his musical genius may have its roots in SAD, particularly since manic-compensatory behaviour can occur in summer months, and this was characteristic of the way Sibelius worked. They feel that perhaps Sibelius's greatest works were composed when he was SAD. The antidote for SAD is simply light. SAD people seem to cheer up when exposed to strong artificial light for six hours or so per day, since it allegedly makes their bodies think that summer has come round again, and their depression lifts. Luckily, perhaps, for posterity, Sibelius's contemporaries would have been unaware of such a simple cure. And neither did the ailment have an affect on the longevity of the composer; he lived to be able to complain depressively about the arrangements for his 91st birthday party, and he died as the grand old man of Scandinavian music as recently as 1957.