Constructive Worry
Constructive worry is a short written exercise done hours before bed, not in bed. Fifteen minutes, at least two hours before you turn in: write each problem down, and beside it the next concrete step. If there is no next step, write down when you will next look at it. Colleen Carney and William Waters set the protocol out in 2006. The honest summary of what it does is unusual enough to be worth stating plainly: it lowered how busy and active the head was at lights-out, and it did not shorten the time taken to fall asleep.
What it is
The timing is as much the point as the writing. The exercise is deliberately placed in the evening rather than at lights-out, because doing it in bed puts the problem-solving in exactly the place that should not contain any. That is the same logic as stimulus control: what happens in the bed is what the bed comes to mean.
The next-step line is the second half of the design. A problem written down without a next move is still open. A problem written down with "ring the letting agent on Tuesday" beside it has been parked somewhere other than your head.