The Undead warlock patron can be found here at DnDBeyond or here direct from Wizards of the Coast.
The subclass is freely available playtest content, so I will reproduce the feature here:
14th-level Undead feature
Your body is now simply a vessel for your spirit. As an action, you can project your spirit from your body. The body you leave behind is unconscious and in a state of suspended animation.
Your spirit can remain outside your body for up to 1 hour or until your concentration is broken (as if concentrating on a spell). When your projection ends, your spirit returns to your body or your body magically teleports to your spirit’s space (your choice).
While projecting your spirit, you gain the following benefits:
- Your spirit and body gain resistance to bludgeoning, piercing, and slashing damage.
- When you cast a spell of the conjuration or necromancy school, the spell doesn’t require verbal, somatic, or material components that lack a gold cost.
- You have a flying speed equal to your walking speed and can hover. You can move through creatures and objects as if they were difficult terrain, but you take 1d10 force damage if you end your turn inside a creature or an object.
- While you are using your Form of Dread, once during each of your turns when you deal necrotic damage to a creature, you regain hit points equal to half the amount of necrotic damage dealt.
Once you use this feature, you can’t do so again until you finish a long rest.
This class feature speaks of you and your body as though they are distinct entities in some sense. It seems clear that when the feature says "you" it is referring to "your spirit", and refers to your body as "your body" or "the body".
In this answer, Ben Barden briefly analyzes this feature and makes the assertion:
Nothing is said about funny things happening with HP, so presumably it’s all coming out of the same HP pool. Nothing is said about effects, so, by default, anything that hit either the person or the spirit would affect the whole. So… basically, they’re both a creature, but they’re both the same creature, who now happens to have two locations they can be targeted from.
I’d like to see a more detailed analysis of this feature so that we do not have to say "presumably" as Ben says in their analysis.
Do your spirit and your body share a single pool of hitpoints while using the Spirit Projection feature?