I'm slightly confused by the use of the word "action" in the text. The section on "Reactions" states:
Certain special abilities, spells, and situations allow you to take a special action called a reaction...
And then there are times where you cannot take actions such as the dream spell which states:
[...] While in the trance, the messenger is aware of his or her surroundings, but can't take Actions or move...
There are also time where something explicitly says you can't take reactions like the Incapacitated condition which states:
An incapacitated creature can't take actions or reactions.
And then there is this phrase from the section on "Bonus Actions":
[...] anything that deprives you of your ability to take actions also prevents you from taking a bonus action.
There is no similar phrase in the "Reactions" section so I am left wondering:
If something, like the spell dream, prevents you from taking actions, but not reactions, can you still take a reaction?