How did a black widow get into my apartment?

I live in southern california, and I know black widows are very common here. I haven been living on the 5th floor of an apartment for 2 years now and never has anything like this happened. I found a black widow hanging upside down between my bedside table and the wall (maybe in 2 inches of space). I have never really been scared of spiders ever. I have delt with them before when I lived in a house, in the garage, or my backyard but never something like this. And it wasn’t until after I killed it i started freaking out, that was really close to me while I sleeping, if it was there over night, or maybe we have been roomates for a while now. And then I start thinking how the hell did it get into my apartment? What are the possibilities? The worst i have ever delt with in this apartment are ants. Now I have been super paranoid that if there could be a random one like this, then they could be anywhere. Could it be if there was one in my apartment, there could be another? should I worry about fumigating? Anything ideas helps.