I'm going to try and put into a context that might help it make sense for you. I do apologise if you find the wording difficult, but I am only trying to help.
You have a baby (congratulations).
From the moment you got the BFP, your thoughts were 'I'm going to miscarry/the baby will have a defect incompatible with life and I'll have to give birth to a baby that will die and it'll be all my fault' and 'my DH will hate me and leave me for somebody who isn't fat, ugly and it'll be all my fault'. Instead of looking forward to seeing your baby on an ultrasound screen, you will be thinking 'they'll find something wrong/the heart will have stopped beating and my baby will die and my DH will leave me'.
'I'm feeling sick and tired. They'll see I can't do my job properly and sack me and DH will leave me and I won't be able to pay the bills and I'll be homeless and he'll take the baby and meet somebody else and bring it up with them as their mother and it'll be all my fault'.
'They say these are Braxton Hicks. I'm going into premature labour and the baby will die and it'll be my fault'
'There aren't enough movements/I haven't noticed a movement for a while (because I've been busy, but I'm not thinking of that). My baby's died'
'There's going to be an undiagnosed birth defect or a stillbirth. I'm going to die in labour'
Get the baby home -
'I can't breastfeed. It's not enough for the baby, even with cluster feeds. I'm incompetent and the baby will starve and it'll be all my fault'
'If I go to sleep, I'll wake up to find the baby has died. If I go and have a bath, the baby will die, a cat will climb in the window and smother them, a fox will eat them, the house will burn down and it'll all be my fault, my DH will leave me'
'If I put the baby in a pushchair and go out, we'll get hit by a car. If I put the baby in a car seat, we'll be crushed by a lorry. Somebody will touch the baby and they'll have an illness which will kill the baby because it's too early for vaccinations'
'If the baby has vaccinations, they'll have a reaction to them and die and it'll be my fault'
'The baby is a little snuffly, not feeding as much/more, is crying/not crying - something's wrong, I'm doing it wrong, they're ill and I don't know it and it's all my fault and everybody will know'
'If I tell anybody I'm having these thoughts, they'll say I'm mad and take the baby away. DH will leave me and take the baby and find somebody else to be its mother'
'DH will leave me, he's just here because of the baby and he'll meet somebody else and they'll be the mum'
'I love my baby so much. Somebody will hurt them and I'll lose them and what was that noise outside? It's somebody coming to hurt us'
'The world's going to end in war or environmental disaster or disease or it'll be horrible and my baby will be all alone'
'DH is ten minutes later coming in through the door. He's met somebody else and isn't coming back, he's had an accident and is dead, he hates me and wishes he'd never met met and, and, and.......'
That's if you can articulate your anxiety and pin your thoughts on it being related to the baby/DH. It can come with all the feelings, the elevated heartrate, gasping breathing/hyperventilation, legs turning to jelly, the fear without a specific thing or situation to attach it to.
I'm getting it quite a lot at the moment. I've been fucked about with redundancy since January, it's a stressful job and I am genuinely terrified that I'll come out of it with nothing/I lose the house. Which is understandable when they've dragged it out for so long, and I still don't know what my finish date or final payment date will be, despite asking. If there's that, a huge time critical workload and my boss is stressed and snapping at me, I can feel the physical sensations well up - and sometimes, I can't move because if I do, I will have my legs go out from underneath me.
However, probably as a result of all the mental unpacking of stuff from my childhood and young adult years following my brother dying in an accident, I'm also getting random bouts of unreasonable anxiety daily. I find my heart pounding as though I've just run for a bus, I jump each time I hear a siren, I'm finding it ridiculously difficult to leave the house and if traffic is heavy or there are lots of people, I desperately want to go home before I get dizzy, fall over and get killed by a car like my brother.
DP is away. In my head, I think he's leaving/not coming back/has met somebody else/is going to stay away because I'm not going to have a job/I'm too demanding at the moment/can't handle me wanting him to come with me if I have to leave the house. Or he's had a breakdown over my being too needy, has had an accident like my brother, there's been an incident and it just hasn't been reported yet....
It's irrational. I'll manage. We'll manage. He loves me and will come back. An accident is unlikely. The one that killed my brother was simply a combination of seemingly unimportant factors that coalesced into a catastrophic event. No great rhyme or reason to it, bad things happen sometimes and it's sad, I'll miss him enormously, but it doesn't make DP or myself any more or less likely to experience the same things.
But it's there at random times of the day and night for no apparent trigger as well as when thinking about the job, bills, DP or my brother. It hit me yesterday when doing something that I love, so I had to sit down and was just shaking, trying to calm down my breathing and keep going. That activity has been the only one I have been able to manage since the accident as it felt safe and others have been able to be there and make it possible for me to get there. I wasn't sure I was going until Friday night, after I'd been encouraged to go by some really lovely people there. I managed it by myself yesterday, as it was relatively quiet out when I left. But I couldn't get home fast enough afterwards, which was annoying as it meant I missed out on the social side. I was embarrassed by feeling like that there - there was no need for it.
And it fucking pisses me off as I resent my freedom being curtailed by wobbly legs, traffic and other people simply minding their own business and getting on with their lives as they have a right to do.
I'm sure that, for me, it will lessen after the funeral and the job stuff is finalised. But for some people, there is no end in sight. And that's a horrible thought.