I heard i loud deep rumble yesterday ...any ideas?

Ok,, so i live in northern ireland ..yesterday i was sitting on my bed reading ...the next thing i know is a hear a loud kida deep rumble... it went on for about 15 secs then stopped.. the sound made me actually stop reading and go look outside because it sounded to me like the world was actually falling apart i expected to go and see the houses in my neighbourhood falling away !! afew of my friends miles away in antrim heard it too and my mum heard it aswell and she as sittin in the living room downstairs...?? please if you heard it or know what it might have been ... im a little scared... :S