From 1842 onwards, Chopin showed signs of serious illness. After a solo recital in Paris on 21 February 1842, he wrote to Grzymała: "I have to lie in bed all day long, my mouth and tonsils are aching so much." He was forced by illness to decline a written invitation from Alkan to participate in a repeat performance of the Beethoven Seventh Symphony arrangement at Erard's on 1 March 1843. Late in 1844, Charles Hallé visited Chopin and found him "hardly able to move, bent like a half-opened penknife and evidently in great pain", although his spirits returned when he started to play the piano for his visitor. Chopin's health continued to deteriorate, particularly from this time onwards. Modern research suggests that apart from any other illnesses, he may also have suffered from temporal lobe epilepsy.