I've had that happen to me twice after coming back from Europe. Each time it was quite painful during the crampup at night and sore for a day or two later. I don't know exactly what causes it but my guess has been electrolyte issues after a long, dehydrating trip. It sucks, though! Treat yo' self in the meantime.
Dehydration sounds plausible. I was intentionally trying to stay slightly dehydrated while in Italy to avoid having to use the super-disgusting porta-potties. ;-) And it was really hot during my workout yesterday afternoon...
Funny I was getting foot cramps all night when I got home and than a major calf cramp. I totally sure it’s dehydration and electrolytes being low.