Little dizzy and very tired. Can sunstroke have delayed effects?

Within 24 hours. When one has a fluid and electrolyte imbalance from sunstroke, it can take a while to return back to normal. The body does not instantly achieve the fine corrections that one desires. That is why it is so important not to start any day dehydrated but rather drink plenty of fluids in the morning and then continuously through the day. Salt intake matters, and one can feel fatigued for 24 hours.