How do you know if it is beginning stages of dementia, or if it's the pain meds making my Mom talk loopy?

While talking to my mom, she'll come up with some off-the-wall comments and then go back to "reality" and I'm not sure what to think. Last week, before I left on our trip to the midwest to visit family, I was talking to her and she said "I don't even know what kind of place this is that I'm in - is it a house or ??? I know I'm not the only one here, because I hear other people talking, but...I don't know...." I was taken aback and didn't know what to say. We then continued our conversation & she asked me about our upcoming trip, etc. It was almost like a momentary "lapse" for lack of a better word. I immediately got her nurse & asked her if she had noticed any confusion, and she said she hasn't noticed confusion, per se, but that she is definitely talking "differently" than she has in the past. She said the doctor has routinely assessed her and that he didn't list anything specific in that regard, and that it could be the pain meds. She said she had given her a percocet about 1/2 hour before I arrived, so thought maybe that's what it was. She then followed me back into her room & asked her a few questions - Mom answered them just fine, and the nurse was satisfied with her responses but said she would talk to the Dr. & alert him of my concerns. I have to mention she also talks a lot about her deceased sister - thinking she is going to come & visit her, before she realizes she is dead, and has mentioned seeing a black cat that wanders the hallways (there is no cat on the premises) and she can't figure out who it belongs to. I don't know what to think, other than I hope it's the pain meds talking because I don't think she or I could handle dementia on top of everything else going on with her.