my cat hid for 13 days

my cat, evie, who will be 4 in may, hid in my house for 13 days without coming out at all to eat or use the bathroom. i thought she had got outside somehow because i searched this whole house for days on end, i never found any evidence of her being in this house, so i thought she got out even though my gut told me there's no way she got out because she has major anxiety & stays away from the door, she also HATES being outside, the only time she'd ever been outside was me holding her and she would dig her claws into my back & cry. just an hour ago, at 12am, i hear 3 meows. i ask my husband if it was a vid on his phone because he was in the bathroom, he said no so my gut said to open the spare bedroom and here comes my baby about 5 pounds lighter than when i lost her, and she's already a small cat. i searched that room top and bottom and i left that door open for at least a week incase she had went in there. i am absolutely positive she did not eat or use the litter at all. her behavior is exactly the same as when she left, she's just thin. my mind just can't piece together how on earth she willingly starved for 13 days, i know she wasn't stuck and i know there's no way she got outside from that room. is this common for cats to hide? for background a little over a month before she started hiding i took her from my grandma's house where we lived since she was 1, i moved out when she was almost 3 and i didn't bring her to our new home until 3 months ago because i wanted everything set up for her since i know moving her would make her uncomfortable. did she hide because she's anxious for 13 whole days?? or is this a sign of a medical issue? i'm taking her to the vet tomorrow regardless but its 1:30am and i'm so worried & confused.