sometimes when I land on the floor I sit down or do something silly and it takes ages to get up and my char goes all spastic?

Welcome to Cortex Command thats a normal part of the game.

arghhhhhhhhh

Unfortunately this isn't how you post on these forums. Try to use complete sentences from now on - Seraph

Spam left and right + jetpack.

spam various combinations of WASD until you get up

once you get used to the movement, it becomes more normal.

also, be sure to pulse your jetpack, and make sure your character isn't too heavy, if you're heavy, you get stuck on everything (general rule of thumb, stay in the yellow)

Pulsing doesn't work with b26 vanilla as far as I know

Pulsing works for getting up.
Not for flying.

this

you still will be more efficient rising up if you pulse.

b26 wrecked my AutoHotkey script that auto-pulsed W though when I was playing cortex command