Many herbs that cause sleep (sedatives) do so by calming down the nervous system or lowering blood pressure. Some even have properties that act directly on the chemicals of the brain itself. Nervines merely relax tension, while sedatives like hops, valerian, skullcap, and passionflower are stronger based off of the dosage you take. Out of the 4, I prefer valerian and passionflower when recommending herbal sleep aids. Hops can cause a "hangover" effect, and skullcap, if overdosed, can cause some very bad effects. Both valerian and passionflower are nontoxic and have no true "overdose" nor a hangover effect. I would suggest lowering your dose and/or changing the way you are taking it. For instance, valerian capsules or tincture are better for anxiety. But the tea is best used for sleep. Water takes in different constituents than alcohol and vinegar, and taking an herb straight has varying effects as well, depending on the oil content of the herbs. Warm liquid has a warm calming effect of its own and absorbs faster into the body. The normal steps is to take the lowest dose and work your way up until you gain the effect you desire. Less is often more. I suggest teas when using them for insomnia. Passionflower is my favorite because it is such a gentle herb and it actually contains a constituent that is identical to our natural chemical serotonin. So it not only soothes the nervous system but it also leaves us with a feeling of "all is well". I've offered passionflower to some of the worst insomniacs I've known and they've slept like babies. I steep it for 10min covered, then give them the option of sweetening with milk and sugar or honey. I've seen no difference in using either.
The great thing about passionflower is, unlike some sleeping aids, it is easily countered with caffeine without hurting you. Great for parents or someone who's job requires them to be "on call". Be sure though that you don't drink or eat caffeine (even "decaf" has some caffeine) any time even remotely close to taking sleeping aids if you want them to work properly.