Synchronities, dreams etc and even paranoia and symptoms in schizophrenia are parts of your unconscious mind trying to communicate with your consciousness. But they talk very different language, so consciousness only sees what something in unconscious wants to "say" in these weaird things and through metaphors that resonate, or synchronities etc. It is healthy to have a healthy communication with the unconscious mind. Especially if you smoke tons of weed, as it can bring out suppressed stuff in more violent ways and cause "psychotic thinking" due to this:
When it comes to schizophrenia or other psychosis(schizophrenia is basically the same, but long term) the thing is that with them the normal process of brains that trims away irrational stuff that doesent fit is disrupted and basically there are leftovers of thoughts that were waaaay out there that were not removed earlier and now they subconsciously effect other thoughts and since these f'd up thought patterns are not removed properly either, but they remain there to disrupt later thinking.
Personally i dont think cannabis fucks up this system, unless there is a slight tendency for temporary fuck ups to the system(=people who get psychosis from weed or other psychedelics, but dont go full out schizophrenics), but what it can do is to induce some of those weird thoughts and if that system doesent work and those are not removed like in regular psyche, then that could lead cannabis to trigger symptoms or make them worse. Im 99.99% sure that this is what the whole cannabis and schizophrenia.
Sometimes if there are enough crap that wants to get out of the unconscious and ego keeps blocking it, it might in the end come up through psychotic issues if you have tendency for some, that is if it doesent let be heard otherwise.
There is an aspect of the psyche that tries to balance out ego, because ego by its nature is focused on stuff related to survival only and this sort of animalistic attitude is not healthy for growth of psyche and only creates obstacles for growth, because part of ego is to keep things that seem to work the same and for your ego there is no problem until you REALLY have a problem and by then the ego is too fucked to realise and you are in hospital.
I dont want to scare you, on the contrary if you realise all this you will also realise that all this is very good and that you should ot be afraid of you own unconscious mind. Im not saying that you should go all in blindly and nothing bad can happen. If you figure this you will learn to see synchronicities etc as a blessing and learn to use them as guides for your ego.
Common stupidly dangerous idea is that you should kill your ego and that psychedelics will help you do that. But you should not kill your ego, you should develop it to be more flexible and to see beyond of it and bow down to your unconscious mind, not think that it is the king. Or well it can be the king all it wants, but the forces of your unconscious are the God and the king should understand and accept this.