Concrete patio with no drainage?

Hi all,

We have a concrete slab type patio outside our back door and the rest of the garden is raised so the concrete goes from the edge of the house to fences on both sides to a wall/steps where it raises up.
This has been covered with decking tiles and gravel. But recently when doing some jet washing the whole area got completely waterlogged and took hours to drain away. This meant there was sludgy water up against the edge of the house for a while!
We're in the process of taking up the gravel and decking tiles to look for some sort of drain but can't find one. Should there be a drain in this situation??

 

Will check for a slope this weekend - but even if there is it will just be sloping into a concrete block wall?

 

Hmmm what a pain!