Have any of you had a strange experience or even an ordinary one where it just questions your own perception?

I have questioned my own peception in both strange and ordinary experiences. The one I would like to discuss is my strange experience, I was 9 years old and my sister was 5 and we both still remember this experience like it was yesterday.
At the time we lived in a two- bedroom house and it was an old house it was build in the 1900's and the cellar used to be a bomb shelter in WW2. Well there's a spare cupboard in my mum and dad's room and there's nothing inside it other than one box , a pair of shoes and it's a really small cupboard, we decided to go hide in this cupboard one Sunday evening because we knew that our dad always goes up to bed for a nap and we wanted to wait until he went to sleep and jump out of the cupboard to make him jump.
This was an unusual experience because when we both went to hide in the cupboard all of a sudden a staircase appeared at the side of the cupboard and you could walk up it. My sister started to go up a few steps but I begged her not to go up because I had this gut feeling that if she got to the top of the stairs we would never see her again.
Luckily she got back down from the steps and we both looked at each other found this experience to be extremely weird so we both gave up hiding in this cupboard to jump out on our dad.

Still to this very day we both still think about this experience and want to make sense of it ?

What could the explaination be because both of us were wide awake , we weren't asleep or dreaming ?