The common theory is that since planning and following through with suicide requires at least a little energy and motivation, some people are depressed enough where even that is too much for them.
When someone starts on anti-depressants a common occurrence is that things get better in two steps, with usually the first being energy & motivation, while the more positive outlook on life comes later.
This is bad because the person is still super depressed, but now they suddenly have enough energy and motivation to think more about how they’re going to kill themselves, as well as actually following through with those plans.
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