Can people chime in whether it is out of the norm to email around midnight?
It is not out of the norm
Should I try to refrain from doing this?
Yes. Despite other answers, I think your worry is justified and you should not send emails at midnight.
I agree with others that the receiver is in control of turning notifications on/off. With or without reason, some people will still get annoyed by your email and you don't want that. They might have notifications on by mistake or because they are waiting for another more important email.
More important than this, if they receive your email at midnight, they might read it! It's very likely that they won't spend much time doing so and are more likely to misunderstand, overlook or forget about it next morning when it's marked as read in their inbox.
Or they might reply to it! You have finished your day and want to take that email from your head and go to bed but, if they reply, I would feel obliged to clarify any questions that they have before going to bed as they are doing you the "favour" of working late for you.
I believe the best time to send an email is when you want the other person to read it, even if this is not guaranteed. I like between 9-10 a.m. when they have had their breakfast and read their inbox but probably not started seriously focusing in any task yet. It gives you the time to sleep on it and maybe modify it before sending it.
Furthermore, some people will flag those who are working at midnight as people with poor time management. I would try to appear to others like you work office hours, even if you don't. Depends on the environment but I think that it makes it easier for other people and more people will think of you as reliable, consistent and professional.