my macbook pro keeps ejecting my seagate external hard drive

I have a seagate 1.5T external hard drive and my mac book keeps ejecting and giving me the red box of doom telling me I didn't eject it properly. It just started a week ago or so, but it seems to happen if I
move my lap top around too much, or sometimes I am just sitting not moving and it ejects. Most of the time it will reconnect but any idea whats happening?? and what is bad about a drive ejecting without you ejecting it?? Am I going to ruin the drive??

Thanks!