Gravity Issue

I connected to a server and it downloaded a load of lua files, and when I got in I flew up to the top of the map immediately. I quit the server and tried to run my own and the same thing happened. I changed sv_gravity to 600 and gravity affected me normally, but when I spawned an object and went near it I flew up again and so did the object. What is going on?! Can anyone shed any light on my situation?

Thanks

Delete your garrysmod folder.