Stimulants cause that edginess and anxiety for me as well, more so with aging ( 41 now). Benzos definitely are great for this kind of edgy, nagging, uncomfortable side effect (effect) that you get from stimulants. As you said, opiates are another solution to this kind of anxiety but for me this rollercoaster effect from the stimulant, opiate combo caused me to exponentially raise the quantity of both substances which I was using. I'm sure that if I was shooting only heroin or cocaine, the quantity that I was consuming would've stayed at a fraction of what I was really shooting. The more coke I used, the more heroin I used and vice versa. I started to make sure to have both and shot the mixture as often as I would have shot only coke which really made my addiction a monster. The synergy of benzos and opiates with stimulants are wonderful especially if you have anxiety issues but it can turn into a massive problem especially when you're a regular user.