Thought I would make my own thread for this because I seem to be making a obvious mistake. I cant find an answer anywhere so others must not be making this mistake

I have a player I added physics to. I used the same method as was posted in another thread:

action myplayer()
{

myplayer = me;

ph_setgravity (vector(0, 0, -386));
phent_settype (myplayer, PH_RIGID, PH_BOX);
phent_setmass (myplayer, 3, PH_BOX);
phent_setfriction (myplayer, 80);
phent_setdamping (myplayer, 40, 40);



while (1)
{
if(key_w)
{

myplayer_speed.x = 5 ;
myplayer_speed.y = 0 ;
myplayer_speed.z = 0;
phent_addvelcentral (myplayer, myplayer_speed);
}
wait(1);
}

The problem is my player falls over. Then he just tumbles around. Is this in my model? Is there a setting I am missing?
How do I keep him standing upright?

Any help is most appreciated.