Day 39 - meditation or hyper aware?

I did the activity for today, a meditation, relaxing all the body parts in turn and remaining mindful. Partly I felt this worked - I was able to focus on the breathing, used a soothing phrase and relaxed my body. But - maybe because I live in such a quiet area - I felt hyper-sensitive to every sound. I was being mindful, letting thoughts come and go, just noticing them, the same with the only sounds, my breathing, the dog breathing, the hum of the computer. But part of me felt hyper-vigilant, like I was in a fight or flight situation, I felt uncomfortable with my eyes closed, as if I was expecting 'something' to happen. It was weird. Has anyone else experienced this?