5 years ago I gave up diet coke and have never looked back. I was trying to cut down on my spending by taking my own lunch to work rather than popping out to buy a sandwich. I noticed a nice metal water bottle on offer when doing my food shop and decided to buy it and save on buying the 3-4 500ml bottles of diet coke I was drinking a day - more if I was driving to a pub or to a meal out.. The bottle paid for itself in a few days!! It was hard, I'm not going to lie, I went through withdrawal, the first few days I felt awful and assumed I was coming down with something, I had headaches and brain fog for about 3 weeks, and if I was not occupied I would just fall asleep. I lost count of the number of times I fell asleep on the bus home and missed my stop, I would get home prepare my lunch for the next day before sitting down as once I sat down I would be asleep and hubby would wake me and send me to bed hours later and I would struggle to get up the next day despite having 10 hours sleep - I would wake up shaky and dizzy - this, along with the tiredness, lasted months.
I will never drink diet coke again, its evil stuff.
On the plus side my bank balance has improved, I feel more healthy now, I have more energy and my blood pressure has gone down! I am now saving more money as without diet coke I have enough energy to walk to work and back, ditching the bus unless we have heavy rain.
Best thing I gave up.