Why do my hands get tingly and stiff upon standing and fingers get straight, thumb straight and pushed in. sometimes in forearms every time i stand up?

Needs evaluation: Sounds concerning for some cervical canal narrowing that worsens if you stand and extend your neck. A cervical MRI can assess for any spinal cord/canal concerns. If you are nervous or hyperventilating, that may play a role also. Neck pain, and hand numbness after a night of sleeping raises more concern for your neck being the source.

Intrinsic spasm: This sounds like an intrinsic spasm. This is usually caused by irritation of the ulnar nerve at the elbow. But your occurs with standing so i would be examined for a lower cervical disk.