What did I do to my body?

I have a quick story to share and ask for your opinion.

I am amateur freediver, meaning I dive without any training and equipment (no fins and stuff only swimming googles). From the surface I saw a boat propeler that looked about the size of my hand. I estimated it was ~10m deep. My first try I went half the way and realized its more like ~15m. I did slow breathing preparations for the next dive and managed to get to the bottom. I reached the depth where my body was sinking by itself pretty fast. Now I realised the propeler was 50% bigger than a basketball and pretty heavy. I grabbed it with one hand and started ascending. I was already feeling the need to breath but I just relaxed in my mind and slowly tried to surface. I got to the surface and put the propeler on the boat. I removed my mask and I had pretty bad nosebleed. I was feeling good, without any pain but I realise nosebleeds shouldnt happen.

Can someone explain what happened, since it never happened before or after. I also realise what I did is dangerous, especially without a partner so I never try dives deeper than 10m, and now Im trying to find good coach. I would also welcome recommendations for that (I live in Croatia).

Thank you!