I think you would be better off trying to break this up into discrete steps. Do you have water bottles? Place one in your room. You don't have to have a glass. You could have two bottles profiled with 50ml of water each. Have some time? Premeasure two plastic bags of SN. When you are ready, you put the SN in each profiled bottle and gently shake. All of these things can be done over days if needed, only mixing when ready.
even if you don't have a water bottle, it is easy to substitute for a cup. I'm not quite clear why you would need to be banging around in the kitchen right before. Everything could be easily and slowly planned for, wait until 1 or 2 in the morning, and there is zero reason you would need to leave your room once you have decided to make your choice.
Trying to act hastily is not a good option.
