This was me 4 months ago with my 2nd baby, my toddler who usually slept really well start having night wakenings & would then be up for the day ( with no nap) at 5am, sometimes before. This really set me on edge as well, I started getting huge anxiety around sleep and would stay awaken all night wondering how the hell I managed to sleep before, like I'd forgotten some formula.
It will get better, you cannot die from lack of sleep ( please, people stop saying this!) I've gotten so much better, I can still have the odd night. But things that helped me.
I took an online insomnia CBT course, this made me realize I wasn't going crazy, it really made me understand sleep & how easily it can be to fall into the anxiety trap around it. Some of the pointers were:
Don't nap, I know this will be hard but something to do with building up your sleep deficit & only using your bed for nighttime sleep. Trying to nap during the day & then not being able to feeds that anxiety round sleep & your negative association with your bed.
Don't obsess over sleep hygiene, I did have a ritual were I wouldn't go on my phone before, drink sleep herbal tea before bed etc. Other than cutting out caffeine it states the obsession over it can fuel your anxiety around bedtime. I also couldn't take any over the counter sleep aid because I was breastfeeding.
My husband took over the night time care of our toddler, so I only had to worry about the baby. She initially wasn't happy, only wanted Mammy, but she got used to it & now only shouts for Dad.
I also downloaded a positive mind app ( I am) reading affirmations throughout the day. I was never one to believe in that stuff, but I figured if I could get myself into this hole with negative thoughts, I could try slowly feeding myself positive thoughts.
It was a really dark time for me, I honestly thought things weren't going to get better, but they didn't, slowly. It sounds strange but I came to an acceptance about it, like said to myself if I don't sleep, I don't sleep. I've not some other nights and I've got up & looked after two kids & haven't died. Lol Positive thoughts about a negative, it helpt my mind be more at peace, and I slept.