Thank you for playing it and your kind words!
In short, Threat Rating tells you how many hit points the threat has AND how many d6s they roll against you.
You can choose to regain psyche when you allocate your successes!
Ex: if you rolled 3 successes, you can apply one to the threat rating (dealing damage to the threat), one to the Objective rating (moving you one step closer to completing the floors objective and finding the elevator), and regain one psyche!
Hope that was helpful! Let me know if you have any more questions!