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.