I'm having a panic attack...

Houses rarely stay empty. They may renovate and sell or rent it out. There is also the possibility of transient people or mischievous teens breaking in because it's uninhabited. That being said in my experience most people who hallucinate like my closest sibling and a few friends I know with schizophrenia or other mental illnesses have a tell that alerts them or close family members and friends that the medication isn't working like it once did. Weightloss and exercise are factors to consider while taking psych meds and there is also an accumulated tolerance in many cases. My suggestion is to make a doctors appointment ASAP but also call the non emergency number to your local police department and let them know you thought someone was in the uninhabited building but got spooked before realizing it could be squatters at which point you're reporting it for an officer to check for signs of a break in or trespassers ect. Let them know you're not sure if there's selling plans or possible renovations but it's been empty and quiet for a while. Then I would contact the close friends and family who you consider safe with your mental health let them know you have concern your med dosage may not be working explain it may also be a weird circumstance that caused your panic attack and ask them to make you aware of any unusual symptoms/ behavior. I trust with help you'll get through this my friend.