OP, I'm so sorry this happened. This scenario is a big fear of mine.
I have a very silly question and I hope you bear with me (sorry in advance, in case you've already thought of this). Do you think there's even a small chance that you didn't finish the drink in full? Water evaporates at room temperature at a rate of 3ml/hour, so you might not have even noticed any remaining SN after waking up 10-11 hours after your attempt. Comparing this method to N, I know the few people who have failed with N had not succeeded because they didn't finish the whole drink and passed out too soon. In your case, you took valium, melatonin and cannabis before taking the SN, so do you think there might have been a small chance you accidentally did not down the full drink in your state of drowsiness?
Again, sorry if this question is silly/sounds condescending. It's just that there are so few possible explanations for this.