There seems to be a lot going on in your post, so I thought I could break it down a bit at a time (I am no expert nor am I trying to judge or seem harsh. In FACT, quite the opposite. I totally empathize on many levels):

1. If your mother supportive of you? She seemed to be invalidating your feelings by just telling you to just "go take a pill". That is painful.

And just as important (or even more so considering your current sitaution):

2. Do you have a roommate agreement / understanding? For instance, when you are gone, your fish will be fed. Or someone will be in charge of cleaning up (split 50/50), or really asserting yourself if you are able by saying, "it's really important to me abc and I feel abc. So could we agree to abc").

You could even have a calendar letting each other know when you will be in / out of town and if guests are expected (you mentioned you left suddenly and then your roommate had people over without notifying you)

It's super hard living with a roommate to begin with, and then even worse when you have no boundaries, rules or understanding. in a lot of cases,it's a disgusting free for all.

3. I've experienced, when having anxiety and panic, the idea of someone "invading" your space, and it can be unsettling, scary and unsetting. Especially if you are not made aware of the situation.

For instance, for me to compensate, I try to "control" the matter by internalizing (blaming myself, being really hard on myself, thinking I shouldn't even be there, etc.) and then super controlling ... cleaning everything, washing everything, making everything look perfect on the outside - and then hiding out (quiet as a mouse so they don't even think I exist because I'm being so hard on myself to begin with).

Good luck!