Ringing in my ears before I fall asleep?

Earlier today, I worked out and I was extremely physically tired. I got home and crashed on the couch. My body was exhausted but my thoughts were still nice and energetic. I remember that it became difficult to open my eyes about 30 minutes into laying down, and their was a soft ringing in my ears, that immediately started to get louder and louder until it was extremely loud and I was frightened and open my eyes and the sound immediately went away. When I closed them within a few seconds of that, it started again. It's like I was falling asleep but my thoughts were still their, perceiving everything happening. I opened my eyes again because this was foreign to me, but then realized if I had just gone with the flow, it might have led to a lucid dream. Anyone know what this is?

Well it could have been one of two things, you know that ringing noise you get after listening to loud music, or for some people it's just always present but you only notice it when everything is completely silent.
Or it could be one of the strange noises that happens when you are transitioning into a dream. I've found physical exhaustion to be a good way to let yourself go into a dream.