Usually the diagnosis in these scenes is drug related but...
It appears to have been a sudden syncope with what it looks like and expensive backpack and some documents under the right hand.
I do not think you guy is a druggy or homeless.
That happens to be in front of the store I bought my wool sweaters 15 years ago, it is a very nice area,, I do not remember seeing derelicts there.
Finally, I am amazed at the attitude of the passers by, the Scots I met all over the country would have stopped.
Great shot, as usual .