One spot of blood and nothing else for days?

my last period was around 10 September , usually my periods start around the first new month , on 25th September (few days ago) i noticed one red spot on my under wear but I still haven't had my period , I;ll wait until 10/15th October just as usuall

but why did that happen? It happened after I had a 5 day water fast (no food or juices at all)

One spot of blood and nothing else for days?
Post Opinion