Interesting, we have almost exactly the same responses to SSRIs! I haven't met anyone else that reacts that way yet! I've been on Fluroxtine (this was my worst), Citalopram and Sertroline - all caused dizziness, coldness, shaking and 'suddenly falling asleep' as I put it at the time; didn't feel the same as fainting. My blood pressure is low at the best of times and I somewhat regularly go into shivering heaps, so your explanation is ringing a lot of bells in my head! Some of them were less bad than others, but they tended to give me all the symptoms of panic attacks (or, like you say, caffeine overdose).
I think I'm quite lucky because the original diagnosis was way back when Dosulepin was much more the go-to drug so was given it straight away (it was called dotheipin at the time). In intervening years, and with this most recent episode, I was first tried on the SSRIs. When a situation happened that was so beyond my ability to cope with, I went back and asked for the Dosulepin as we knew it worked for me and I didn't think we had any more time to mess around. At first I was put on 75 which helped control but didn't stop a big breakdown and then it was put all the way up to 150 again.
One thing I've noticed is that younger doctors tend to have much less experience with this drug, and they seem to want to start me on a lowish dose. When I saw the older doctor at our practise he was quite specific on the 'you need more' aspect. He was not wrong!
I reduced because I was having some side effects; tiredness being one and very acid stomach being the other (I find them hugely acidic). One problem I have is that one of my major depression symptoms is tiredness so it's hard for me to know whether I'm tired because of the illness or the medication!
Anyhow, sorry to go on a bit! I've found among my friends it's an unusual drug to be given, so I find your story fascinating!
I'm really glad the first few days have gone well and really hope it continues for you! Part of my is resolved that I'll now be on these for life but you never know; I might try again to reduce at my next review in October. Once again, good luck with it - best wishes to you!