19 month old angel sleeper turned into a monster help!

[KTD27]

So my DS is nearly 19 months. We sleep trained st 6 months gently but he took tonit like a pro. Easy to settle and generally has been ace for a year. BUT
suddenly he's become a total monster. Won't lie in his cot, forget self settling, if he wakes at night he is hysterical for hours unless I sit and rock him and the rocking has become his way of going to sleep. For nap today he was rocked and then put in his cot. Last night he ended up with me after screaming for two hours.
He just wants to settle on mummy and drift off.
Has all his teeth except for his last molars. Also been sick with nursery winter bugs so off his food and generally a bit meh for a month or so.
Is this separation anxiety / sleep regression combined?
Do I give him what he needs/ wants etc?! Or try to tough it out! Only possible thing to add is that he has a heart condition (which we didn't know about when we sleep trained or never would have) and I worry that his hysterical anger may set things off.
Ahh! Tearing my hair out!
Any tips or virtual wines gratefully received

That heart condition would be the critical factor for me. In that situation I just wouldn't do any 'tough it out' methods that involve any crying.

In your situation i would embrace cosleeping. Or if cosleeping is unsafe for you, try attaching a cot to your bed as a sidecar. That way there is no need for baby to be distressed.

I'd also suggest introducing a comforter object, if you haven't already.

He has one but thank you. He has weirdly stayed asleep all night tonight and of course I'm awake like a well trained puppy. He's shuffled about a bit so he knows he is in his cot. So far so good.
I think I'll continue to give him what he
Seems to need and hopefully it's a phase he falls out of as quickly as he fell into..:
Here's hoping