So I wanna ask you all what to do in this situation? I'm super confused, like really confused.

I'm 24, doing a master's and I work part-time as a teaching assistant and PR for the dept in Phuket. Been here almost a year, I know the professors and folks in the office okay but I'm not a full-time staff. My tasks are prepping slides, coordinating students, and teaching a few small topics to the lower years. Actually I only teach 2 hours/week, but I have quite a lot of responsibilities.

Yesterday around 2:30 pm something happened. I was in the middle of running a lab class — 12 students doing experiments, like setting up tubing, dropping reagents, timing things. One hand on a pipette, the other holding a little blue notebook. Leaving at that moment was really hard because some experiments weren't finished; you can't just put your hands down. That stage would've taken another 15–20 minutes.

The head of the unit messaged on LINE: "Can I talk urgently?" No extra details, nothing about how urgent. I told the students briefly, "Be right back, I need to step out to talk to a professor about something work-related," and ran out. I was on high alert and also felt weird — some people still had unfinished experiments. When I got back a few students asked, "Why did you leave just then?" I felt really awkward T_T

At the head's office it was quiet. They spoke fast and said there's a budget thing and they wanted me to be the contact person for a partner. The catch was I had to go meet the vendor in the evening (around 6:30 pm), which clashed with my teaching. The head said, "It's fine, I'll handle it myself then," but in a tone that felt like an order more than a suggestion. I stood there baffled and blurted out that I needed to check my schedule first.

They softened a bit and said if I can't do it they'll assign someone else. I was like... wait, what about the tasks I've been handling all along? I started feeling like I'm expected to sacrifice my study time to do extra work outside my hours, or maybe I'm overthinking. It felt like being tested abruptly without a polite prior discussion.

I went back to class and some students asked, "Are you okay?" I kept a neutral face but inside I was angry, confused, and guilty for leaving mid-class.

Sorry for the long post, but I wanna ask: if your boss gives urgent orders with no details while you're supposed to be teaching and students are waiting, how should you respond or handle it politely without being taken advantage of? Should I talk to the boss later to set clearer boundaries? Or just be flexible depending on the situation? Or am I just worrying too much lol

I'll update later. If anyone has direct experience or perspectives, please tell me — what should I do?