Do Mermaids exis?Because afew weeks ago i was swimming with a friend and i think i saw a mermaid!?

i was swimming and all of a sudden i felt a gust of water hit me and then i saw this tail quickly dart around us a few times then up the beach and off into deeper waters we tried to follow it but it got away and dove down it stayed under water for a long time and i was scared to death my friend said i was paranoid but i know what i saw and dolfins and sharks dont have arms and especially dont have hair on their heads!!!!!