Hmm...I don't really get what you mean, sorry. You mean you slide - the camera or you? And..you were using devcam right, not flying camera? To use the devcam, enable alldev/ devmode, press the tilde key, type in:
debug_camera_save
then press enter and type:
debug_camera_load
and press enter again and then press the tilde key again.

Now, to move the camera, hold your middle mouse button and press w, s, a, d to move it front, back, left, and right. Hold your middle mouse button and press r and f to move the camera up and down. Hold the middle mouse button and press g to rotate the camera. To speed up your camera movement, hold down your middle mouse button and scroll down. To slow down your camera movement, hold down your middle mouse button and scroll up. And to go back into your first person view, press the tilde key again, then type in camera_control 0
and press enter. Then press the tilde key again.