My toddler usually wakes up from sleep crying badly. She even throws tantrums and runs around the house, unable to explain why shes crying. Why does she behave like this after waking up?

It seems like your toddler is over simulated during the day time. Thus it's affecting her during the sleep which may cause 'nightmares' Cut down on screen time 1-2 hr before bed time. Cut down on sugar after dinner time as sugar gives them energy.

I had the same problem recently. Its really bad.