Oh how I hate how Garry's Mod makes me lag for no reason.

Every other game I play, involves little or no lag at all. However, when going onto Garry's Mod, it's an entire different story.

Like, here is a scenario:

Quote Originally Posted by Story
So here I am, playing in Jetboom's Zombie Survival server. I get many a kill in the beginning of the game, I get up to the Inferno (lol) gun.

Can you guess what happens next?

While I was walking toward our soon to be cade, all of the sudden...

I stop. I am like what the fuck, then it puts me back 4 to 5 spaces back, and plays me walking forward slowly. This is what is known as "Phantom-walking". You see yourself replaying yourself walking, while other people see you standing still. This is lag at it's finest moment.

And then what happens?

I get mauled by ONE HEADCRAB.

Seriously, not cool.
I never had any bad experience with lag on any other game, except the online games from Steam.

Any ideas why it happens?