Hi, if you've been on citalopram for so long and are experiencing withdrawal symptoms, don't lower your dose any more for a few weeks. When your body has adapted to 5mg and you no longer suffer from changing moods and lack of energy, consider getting some kind of tablet cutter and going to 2.5mg/day.
Don't alternate doses eg 5mg one day, 2.5mg the next, as this might exacerbate any side effects. I still don't know why doctors advise this. Stick to a dose for several weeks, then reduce to the next one down.
Withdrawal effects don't come to everyone but they can be extremely hard to deal with. In fact it's a testament to how well you're doing that you haven't given up trying to withdraw. Don't withdraw too fast; it's not a race. But well done for being able to do this and feel proud that you've coped so well.