cat hiding under bed recently

for context, i live in a studio apt. it is fairly large and i let my cat in the hallways sometimes and i have cat trees, windows, and plenty of toys.

my cat used to greet me every time i walked in but now she only does it like 2/3 of the time. she used to come out any time people came over because she is very social. but for the past 2ish weeks she has been hiding under the bed for hours at a time, including when i come home and when people are there. under the bed she is usually in an empty box and lays with her head down.

this is so very unlike her that it is a little concerning. and there havent been any major environment changes or anything.