Originally Posted by
Iride01
Not adequately hydrating during and after the ride will cause you to feel excessively tired too. It may not even be immediately after the ride and it might last for days before you feel fully yourself again.
You can check for that by weighing yourself before and after a ride. If you are losing a lot of weight via sweat, then simply drink more during the ride.
Could be low electrolytes too, and/or depleted magnesium. I'd ask the doc to make sure the labs include those (I say this based on personal experience).