What's the best Injection to Slowly Fade Away?

[Enditsoon]

I'm probably not going to do anything, but I want the option. I want something I can inject that will kill me over the course of 15 minutes to two hours, preferably without a ton of pain. I want some time to think as I go.

The Wiki is confusing and I'm in a lot of pain right now so it's kind of hard to read it. I'm sorry for the trouble.
-Thanks!

(Pills fitting this description would also be okay.)

 

[Hunter100]

Heroin (especially if you do not have a tolerance) it is a warm wonderful feeling. But it is reversed with narcan if someone is found in time.

 

[Ark]

I am not an expert but each time my kids OD'd by injection it was with Fentanyl. They were brought back with Narcan but both told me that with F it is much stronger than H and they didn't know it was F and the same amount of H wouldn't have killed them. They also both said it is incredibly fast and peaceful.