OP.
First, sending you empathy. What an awful situation to be in.
Second, if you are unfit to work then you cannot work. You MUST take sick leave, and explain to your boss precisely why. I reached a crisis point like this when I was suffering severe short-term memory loss. I forgot to turn up to a lecture (that I was delivering). That's unheard of for me. I'd be talking to someone and I'd forget what I was saying mid-sentence. I spent half my life searching for misplaced items: the memory loss was causing me to lose practically everything. I thought I was losing my mind, or starting early-onset dementia, and I was so frightening. I also (probably rightly) assumed that if this went on there would be serious questions raised about my professional competence.
I've been carrying this condition around with me almost all my life, but it was only when I became very sick like this that I realised someone was seriously wrong with me and this led me to receive the diagnosis. The cause? A trigger (sexual harrassment in my workplace).
The diagnosis was like a lifebelt for me. PTSD IS eminently treatable.
Recovery did require a fairly protracted sick-leave. But EMDR therapy was the real game-changer. It's completely changed the way I interact with people and enabled a clarity of vision. It can't remove the trauma from your life, but it can strip away the emotion and enable a real objectivity. CBT is the NHS's go-to, however, so you need to know it's available and actively request it. You also need a good therapist.
I sympathise, OP. I was where you are now, albeit the symptoms manifested differently. It's truly awful. The good news is that you can recover. I'm living proof. For the first time in my life I feel free from something I didn't even know was affecting and constraining me in the first place.
Wishing you hope, health and happiness.