Sounds like stress to me. If you normally go to bed early, say before 10 PM, then the late night could add to the problem. Either, especially both, could cause you to have palpitations, and high HR. Try to deal with your stress, remember thing will work out, give it your best and don't worry about things.
Hi Vicki -
I think what you have there is the perfect storm for arrhythmia (the benign variety, anyway).
Caffeine before bed never helps (and it actually stays in your system and can affect you for 12+ hours).
Alcohol is a brain depressant but a heart stimulant.
And lack of sleep can always mess with my heart rhythm.
Add to that whatever stress you might be feeling about teaching and I'm sure that's your cause.
Next time your heart races try the Vasalva maneuver (Google it). It's easy to do and helps a lot of people get their heart back into a slower rhythm.
Lack of sleep often leads to heart arrythmias for me, too. The other thing that sometimes happens when I'm focused on something and lose track of time is that I forget to drink water and get a little dehydrated, which also messes with my heart rhythm. Could that have been the case for you? I also find that sometimes when I'm anxious before falling to sleep, I actually start dreaming about a bad outcome of the situation or have an altogether unrelated but upsetting nightmare and wake up with racing heart and/or palpitations. Visualizing being on a beautiful, sunny beach for about 15 minutes before bed seems to reduce the risk of wake ups for me.