The way I envision it is that those times we are stuck in our own head, we are unaware of the timelines and how they are moving. Deja Vu and Mandella Effects are related to our thoughts shifting our timelines. There could be an infinite number of timelines we could travel down, but going down each one is setting a chain of events that plays into all other individuals we encounter etc. Basically everything that can and will happen is always happening and always will be happening.