When you rest in Dark and Darker, two things happen. 

You Will Regenerate Any Recoverable Health

The first is that you will regenerate any Recoverable Health at a rate of 1 health every two seconds. 

When you take damage, 50% of the damage you took remains as Recoverable Health, unless the damage was a Damage Over Time, which leaves no Recoverable Health behind, or the damage was from casting a Warlock spell, which leaves 100% Recoverable Health behind. 

If you rest at a Campfire, you will also heal a certain amount of Normal Health per second, which is 3 by default, and can be modified by the Physical Healing stat. Of course, if you want to recover faster, you still need to use Dark and Darker Gold to buy some potions.

You Will Regenerate SP

The second thing that happens is that you will regenerate Skill Points, or Spell Points, or SP. 

Each recoverable skill and spell is assigned a “tier”, which determines how much SP is required to recover it. Each level of this tier adds 100 required points. And a Tier 1 Spell like Bless requires 100 SP to recover one cast, while a tier 6 Spell like Chain Lightning requires 600 SP to recover one cast. 

Second Wind and Blood Exchange have hidden tiers behind the scenes. Second Wind has a tier of 6, and Blood Exchange has a tier of 1. 

SP Restoration Methods

But not all SP restoration methods are created equal. 

Resting on the ground grants 8 points every 3 seconds. Chorale of Clarity grants 2  points every 3 seconds. Resting at a Campfire or Meditation grant 34 points every 1 second. And the Potion of Clarity grants 17 points every 1 second. 

But something is off. If Resting only gives 8 points per tick, why does my Cleric’s Bless restore 1 cast in 5 ticks? If I divide 100 by 8, I get 12.5 ticks, not 5! The answer here is a hidden modifier to SP restoration: Spell Capacity! 

Spell Capacity

For each point of Spell Capacity, you get 1 more point per tick. 

So, for default Cleric, who has 12 Spell Capacity, they get 20 SP per tick, which makes Bless restore in 5 ticks. This also explains why Wizard only takes 4 ticks of resting to restore a tier 1 spell. And why they only take two ticks of Meditation to restore a tier 1 spell. 

This Spell Capacity modifier only seems to apply for spells, however. No matter how much Knowledge and Spell Capacity I put on my Fighter, Second Wind always takes 18 ticks to recharge at a Campfire. Second Wind also will not restore from normal Resting, Clarity Potions, or Chorale of Clarity. 

So, it can be assumed that Spell Capacity, Normal Resting, Clarity Potions, and Chorale of Clarity are all hard-coded to only benefit Spells, and not Skills.

Finally, I would like to remind you that:

• Meditation is weird. Its duration scales with Spell Casting Speed, yet it always seems to give 17 ticks (16 from time, 1 from the “instant tick), regardless of duration.
• Tickrate in general is weird. Some ticks are much faster or slower than others. It might be some weird server-to-client communication is.