Would practicing for a marathon and or having a sugar high cause delayed headaches the next day?

I was practicing for a 42km marathon walking and jogging and I felt fine when I finished. The only thing that hurt at all were my legs. When I woke up the next morning I had headaches all day. This has happened once before, but I walk on a regular basis. Could the extra distance be responsible for the headaches. Also I am a diabetic, and unexpectedly I had a high sugar part way through. Would that cause delayed headaches?|||dehydration is my guess. I get killer headaches when I am dehydrated