I would highly suggest only using Sleep Powder in cases where your insomnia is particularly severe. Using Sleep Powder routinely can cause a human to become dependent on it, and in any case, even one use can be risky. If you aren’t extremely familiar with your own body, it may be difficult to figure out the proper dosage. Incorrect dosages may be either ineffective or far too effective, depending on the situation. There have even been cases where the patient was incapable of falling asleep and wound up experiencing vivid hallucinations instead.
Granted, it is an effective sleep aid when taken responsibly. It just requires working with a doctor or, as I’ve mentioned above, an inordinate amount of knowledge concerning one’s own body to figure out what “responsibly” means. But when taken, it results in deep, restful, and (at the risk of revealing far too much about myself) essentially dreamless sleep.
Sing, meanwhile—as well as similar, non-chemically-based sleep moves (Grasswhistle, Lovely Kiss, Hypnosis, and even Yawn)—are indeed far easier to control. More specifically, while Sleep Powder users do consciously manage their quantified output but have no control over the specific qualities of their powder’s chemical potency, Sing users (as well as those using any of the other aforementioned moves) have complete control over the effectiveness of their techniques. Thus, not only would a Sing user lull you to sleep, but they’ll also be able to regulate their singing at a moment’s notice if they feel that they need to adjust. However, Hypnosis users, particularly members of the drowzee family, are preferable because their psychic abilities also allow them to monitor exactly how effective their techniques are. (It’s just that neither drowzee nor hypno should be used in proximity to children or on children directly, as their powers may induce pokémonitis instead.)
Of course, it’s also wise to consult with your doctor about a more long-term option. While these moves are great for treating insomnia on a night-to-night basis, it’s far less risky and far healthier to determine the root cause of your sleep issues and treat those. That way, you avoid developing a dependency on any of these sleep aids (all of them can be habit-forming), as well as any adverse side-effects your condition may have on your overall health. It may even be as simple as using a pokémon with Aromatherapy or Sweet Scent to reduce stress instead of following the procedures outlined above.
Good luck, anonymous.