The end of an interview is always a bit odd. Even when the conversation went swimmingly, it can be unclear what’s next.
Two quick recommendations:
1. Ask “What’s the next step? Do you need anything else from me?”
This hopefully will guide you as to whether they will be asking you in for another interview, and more importantly, when. Either way, it’s a lot better than simply waiting around not knowing anything.
2. Make sure you have the interviewer’s contact details. Ask for a card. Or just write it down. Then send your thank you email when you get home.