I've just been Googling, he took an overdose of 50 Ibuprofen in 1999 but I don't think that explains what we see on our screens - there must be something else
Just turned it on to see what you meant and I agree sounds like he has had a stoke... Nothing in the news recently or past couple of years about it though....
On 31st December 2008 Smith appeared on Celebrity Mastermind. He was noted to have an issue with his speech which sounded as though he had suffered a stroke. People linked this to his addiction to ibuprofen in 1999. However, Griff Rhys Jones had already stated in an earlier television appearance that Smith was suffering the effects of the early stages of Parkinson�s Disease