you need to drink a couple of bottles of pedialyte( get the small bottles/ 6pk) the night before and bring a couple with you for the ride. you most likely depleted your potassium stores/ and if you drink too much water without replacing the sodium you were def out of balance( overhydration with water but low on sodium i think they call it hyponatremia) anyway dan had the same prob during wrestling season last yr( they call it salty sweating syndrome) and the sports med doc diagnosed cheese its( haha i know i didnt believe it myself) and pedialite to replace the electrolytes.. he had calf cramps several times and had to forfeit 2 matches and couldnt walk for 2 days afterwards.. not a fun thing… if you sweat too much and dont replace/ or dont preload in prep for the ride that can easliy happen.. also calcium suppliments can help with muscle recovery.. on a daily basis just get the calcium w/mag and use ca citrate ( easier on the gut)
dave you are too old for that many miles anyway… stick to the track