Is the imposter syndrome normal when you start your program?

I’m starting a part-time PhD in Epidemiology this summer (a bit unusual; most students begin in the fall). I work full time at the same university in a research lab that touches on Epi but is a separate field. I’m using the university’s tuition waiver to keep the arrangement financially viable while maintaining my full-time role.

A faculty member in the Epi department recruited me after reading my master’s thesis and will serve as my mentor throughout the program. My M.S. is in Quantitative Psychology; so while there’s methodological overlap, I’m stepping into a field I don’t have formal training in.

I feel like I’ve walked into a program I know very little about, and the imposter syndrome is hitting hard. Is this a common experience, especially for people coming in from adjacent fields?