A few points.
Everything is energy. It can't be destroyed & it can't be created. It can only change form.
Once folks really understand this truth, then one realizes a universe can't have a beginning or an ending. It can only keep changing form - just as it is doing.
As for you being your own imagination. it would be more accurate to say you, Eri, are a unique reflection and interpretation of all that is around you. Your mind and thoughts are unique reflections of a multi-faceted, multi-dimensional, universe.
You are composed of everything and everyone else. We all are. We couldn't exist otherwise.
That's one of the wonders of duality something which manifests all the way down to quark parity.