All of our horses usually lay down and go to sleep around noon when the sun is highest and sleep for a few hours. It is quite a sight to see, because they do it at that time, every day that it is sunny. I've had family and friends freak out because they see them laying lie flatties. I wouldn't wan't to start making him too insecure to sleep in front of you, so after you do the check to make sure he is still alive, probably be a good thing to keep the panic screams to a minimal. ;) With my gelding I can and have walked out to him in the pasture and sit down by him. When the sun is just in the right spot, it is so nice that I can't blame them for all just keeling over.
I have a picture where our oldest mare, who is 20+ years old, just decided to lay out flat. That roused a bit of panic, but I just kept an eye on her for a minute and she moved and that was good enough for me.
For fun, I attached a few pictures of said flatties. First one is the old mare, and second a mare who is only 5 but so wide her legs hardly touch when she lays flat.