The description of the Haste spell concludes with:
When the spell ends, the target can't move or take actions until after its next turn, as a wave of lethargy sweeps over it.
Could the target still use a reaction (to, say, throw up a Shield spell if needed) or is a reaction considered a type of action?
Since the spell depends on concentration, it could end unexpectedly if the caster loses concentration on it, leaving the target in a perilous situation.
Jeremy Crawford confirms this on Twitter.
Clint McReynolds @CJMcReynolds
@JeremyECrawford After Haste ends, PHB says target can't move or take actions. Does this include reactions? Advantage to hit target?
Jeremy Crawford @JeremyECrawford
Actions and reactions are different. If an effect, like the haste spell, shuts off one, it doesn't necessarily shut off the other. #DnD
In the PHB, the Incapacitated condition differentiates between actions and reactions:
Incapacitated, PHB 290
An incapacitated creature can't take actions or reactions.
Actions and reactions are different.
If you had haste and fly on (concentration can be dealt with via potion, buff from ally, magic item, etc), and someone cast a dispel magic on you, you can still catch yourself with a feather fall.
If you were frozen with lethargy, you can still muster the "energy" to cast shield, hellish rebuke, absorb elements, or even counterspell, and perhaps you can narrate it as one desperate wave of the hand and a breathless incantation.
Ending haste does not incapacitate you. It just makes you lethargic and unable to take actions.
No.
A reaction is defined as "a special kind of action" in the rules (PHB, p. 190), and therefore is governed by anything affecting actions. It's special-ness is not defined as to be immune to action-depriving situations.
Furthermore, it would be odd for your extreme lethargy to prevent you from intentionally taking actions, but let up in a flash when you want to take a reaction, and then return.
I understand that Jeremy Crawford rules differently, but his Twitter rulings are no longer official and this has not been addressed officially.
