I know you said you had some electrolytes, but a lot of electrolyte supplements & additives don't really have as much salt as what you need (it's 99% of what you lose in sweat as far as electrolytes go). I put 1/8 tsp of salt in my water bottles and choose carb supplements that also have some sodium, like powerbar gels.

I get chilled very easily after rides, too (even if it's not too cold out). So, like everyone else said- could be hypothermia.