I have taken Zopiclone on and off for a while. The doctors, now, are not keen on prescribing them as all the Z drugs, as they call them, can be very addictive. I once had a discussion about how dangerous could it be to be addicted to a good nights sleep!
Due to doctor reluctance I am not taking it at the moment. They do have side effects and drowsiness is an obvious one but, by their very nature, I would assume that feeling depressed might be another. I have never had any side effects. My dose is very small and I even cut that in half! The main side effect of that one is dry mouth. If I took more of it then depression might be another one? You could try cutting the dosage?
I never need help with going to sleep. It is those middle of the night wake ups that are so awful. My doctor was all for me trying the herbal remedies and he also suggested Phenergan which is an anti histamine that causes drowsiness. None of those worked for me but I have good reports of them.
Sleep disorders are very common and very varied. Mine, I believe, is caused by anxiety. I worry over forgetting things that need to be done and all sorts of other silly things that do not seem silly at 3am! If I write things down before sleep I will still wake up with another thing and fret about it. I problem solve for England when I wake up too. At the moment I am on Amitriptyline which is now used as a pain killer but was marketed, first, as some sort of anti anxiety medication. I do get sciatica and other aches etc when I wake up, which also prevent me going back to sleep, so the doctor thought they would help. My pattern now is to take it before bed, I still wake up (!) but Co Codamol will help me go back to sleep. I am now completely used to waking up in the middle of the night but cannot bear to stay awake waiting for sleep to come.
My advice would be to delve into why you are not sleeping and deal with that. I am, when things permit, going to go back to a therapist, who offers hypnosis, as all the research I have done leads me to believe it would be the best for me. She uncovered a load of childhood stuff that is at the root of my anxieties. I am, now, able to talk about them and so I think a few more sessions might give me the tools to sleep more than 4 hours in one go! Talking of 4 hours - there is a theory that in cave men days we only slept for 4 hours before waking and then going back for another 4. That theory helps me feel better at 3am