Root of existence

Hello Rabbi, a close friend of mine was diagnosed with schizophrenia. This led me to realize that my five senses are questionable and therefore any intellectual/emotional conclusion is questionable (since the information I receive with the help of the five senses is questionable).
In the context of faith – any intellectual claim (i.e., every creation has a creator) or emotional/experiential feeling {a Khazar king who dreamed of God} is questionable.
The only thing I am certain of is existence, even if the dimension in which I exist is not "real" in terms of reality, it exists in another way (such as a dream, imagination, etc.).
I tried to understand whether it is possible to get to the root of existence and prove that there is a beginning and a God, or whether it is impossible.
I thought about the concepts of beginning and time, whether time is something that exists on its own or not.
I read as much as I could find, but I still didn't understand what the meaning of the word "nafka" was. We tend to combine the concepts of beginning and time. But, even if time had a beginning, maybe the beginning of existence doesn't depend on it? (Maybe the world existed apart from time?)
In short, I'm confused. If the rabbi could direct me to some article (of yours) or some answer from which I can proceed, because I haven't found a clear course of action.