I think you need more salt/electrolytes in your drink. Give that a whirlI got some energy gels with sodium, and I take one of these at the half way point of my long runs, with water. I take water on the way round, and three additional regular gels.
I try to finish my runs near a shop, and I often get a drink at the end, sometimes a sandwich, followed by a 1km walk home during which I stretch and stuff.
It's not a big problem really. Just on a couple of occasions I've felt quite bad. A few weeks ago I felt about to faint whilst showering, so I quickly dried off and lay down and felt much better. As I say though, I don't think it's a serious issue - just something to try and avoid if possible.