Hello Bob - sorry to hear you're going through hell taking this drug :( It sounds like you were adjusting the dosage at a rate that your nervous system/mind didn't like. :( Unfortunately a lot of doctors don't realize how powerful SSRI's are at what may seem like an insignificant dose of 2.5mg! I wish they'd stop suggesting alternating doses as it just doesn't work for a lot of people..
When I discussed with my doctor [GP] about want to come off 10mg Citalopram for Buspirone, he said I could just stop the Citalopram and start Buspirone the next day. I'm pretty sure i gave him a "are you serious?" look.
I think taking the 2.5mg should be your plan to allow your nervous system and brain stabilize. Heck - stay on that dose as long as it's not causing any ill effects. And if you want wean off the drug at a later time down the road, it should be easier to do so at 2.5mg.
BTW - here is some information that you might want to read that I've re-read since taking Citalopram 4 months ago:
Tips for tapering off by 10%
Chart that shows any dosage decreases below 10mg can be significant:
Good luck and hopefully you'll start to stabilize soon.