Chris,

I would bet dollars to doughnuts that the cause is
the sore throat and the oncoming virus.
Funny how you can be sick for days before you have
any recognizable symptoms. I'm thinking that the
exertion of your 230km ride took its toll, your body
was fighting this virus (unbeknownst to you) and something
had to give.
I think that seeing the doctor won't hurt, at the
least it will give you some peace of mind.

Marty