Edit: Just realised its a common issue, so no real stress

So as soon as i click the realms button (from the main menu) it comes up with:

Invalid session

Please try restarting Minecraft

I've restarted, logged out and signed back in no luck. I'm not sure if this is a realms problem, or if my files have randomly corrupted or something else, but please get this patched or let me know how this can be fixed.