So I did a 40mi ride with a friend. Hot out (over 80F which is abnormally hot for us. Without any joking, we aren't used to riding in that kind of heat)...he didn't drink enough...and we did stop for some lunch half way through. He had one water bottle in three hours...we pushed pretty hard...and when it was done we stopped at my place and he just felt like cr*& and it was a full 30 min before he really caught his breath to the point of relaxing. He wasn't gasping for air...but was breathing abnormally hard for being done. He was wiped and had to take it really easy. Not bonked. We finished reasonably strong. No point in asking about going to the emergency room. Not my call. Nothing came of it. He's fine but he took the next day off from riding. Anyone experienced this kind of a thing?