Ab
I put a simple, cheapier cylometer on my MTB. Since I"m riding a virtual RAAM, you better betcha EVERY mile on Every bike counts (ok...maybe not the "i'm tooling around in front of the house to check a change I made" rides) I think I paid $15 max for it. It tells me max sp, miles travelled, and ATM/Stopwatch. When Snow and I go MTB'ng, those miles count!!
I'm with the "if I'm riding, I'm counting" train! As for being tired, you didn't eat breakfast which would sound to me like you didn't have any fuel in the tank. And when the tank is empty, you're pulling energy from the wrong areas of your body and it takes a while to rebuild that. MommaMac says, don't skip breakfast!
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, champagne in one hand, strawberries in the other, body thoroughly used up, totally worn out and screaming: "Yeah Baby! What a Ride!"