Should I notify students that I've interacted with after getting sick, by email?
Either you infected them, or you didn't. Sending an e-mail about it will not change that (enough time has passed that telling them to wash their hands now will make no difference).

Therefore, it only makes sense to send an e-mail if it turns out to be something where early treatment can make a big difference, or where ignoring it can do harm. (IIRC, this year's flu is an especially bad one, and students might be tempted to dismiss it as just a cold. It's good to remind people that the flu kills and that they need someone to check in on them every few hours.)

Technically, an early warning might also let them avoid people until they are sure they aren't infectious, but in practice that is unlikely to happen as "I was in the same room as someone with fever earlier" probably won't be accepted as a valid reason to skip class...