Dog drinks a lot and then vomits. What could that be?

We've been on vacation in Italy since yesterday, and since then our dog (a 4-year-old Maltese) has been drinking excessively and has already vomited twice today (from bile). What could this be? And should we be worried?

My dad says it's just the stress of there being a lot of dogs around us because we're at a dog campsite.

(She also wants to bark a lot, but of course she isn't allowed to)

Thanks in advance for your answers 👍😊