Its okay to feel sad.
It’s okay to feel angry.
It’s okay to be scared.
Negative emotions and feelings are natural and most definitely healthy if something negative happens.
It is not possible to be positive at all times and that is okay.
What is beneficial of having a general positive attitude in life is that when you are down you will be able to rise again instead of staying down in the depths of despair.
Don’t be discouraged by the whole “be positive” notion if you are feeling negative. You are human and will feel down sometimes.