FAQ from that website:
Is Don ill?
It would seem that he is, though all 'official' statements have denied any possibility of an illness. Rumours circulate, who knows which are true.
In the BBC documentary The Artist Formerly Known As Captain Beefheart John Peel stated that Don was suffering from 'a long term illness'. The 1994 poetry readings and Anton Corbijn film would also suggest that Don is unwell. This long term illness seems most likely to be Multiple Sclerosis, but this is merely speculation.
His gallery and any friends still in contact with him continue to deny that he is in anything other than top shape and say that the rumours of ill health are probably just exaggerated speculation caused by Don's reclusive nature. What little evidence there is for the rest of us to go on would suggest otherwise, however.
Don's illness, assuming that he is ill, is another big reason not to bother him needlessly.