Type 1 antihistamin REDUCES sleep quality, such as Zonat. It also give you a mild hangover(waking +4-5 hours), which is a severe hangover if the problem is low sleep quality.
Its prescribed as a alternative to insomnia, but won't fix it if its recurring, but it will partially fix that night.

Melatonin wakes you up after 4 hours of sleep every single time if the dose is too high. Also you build tolerance over 2-3mg per tablet.
Reduce dosage.

Hypnotic sleep drugs such as Imovan has very strong tolerance buildup. Even at 7,5mg the 7th tablet is nowhere near as potent as the first one
Even if you take half pills each 2nd week, the last pill is nowhere near as potent as the first one.

>how bad
pretty bad compared to fixing your sleep apnea