You can have several sequences (aka timelines), one with nothing in it. AS harm says, double click the “sequence” icons in the Project window to open all sequences and then tab between them.
Also the timelines can have scroll bars if the height of the timeline is smaller than the number of tracks, hiding some of your tracks.
Worse case is that you did a lot of work and said NO to “Do you want to save…” when you closed Premiere down.