I was using my laptop and suddenly got this notification "Intel Rapid Storage Technology SATA Available Disk: Removed" and I can't find my 1TB hard disk in my laptop.
The SSD is still there but can't find HDD.
Laptop : Acer Nitro 5 AN515-54-76NB
I7-9th gen, 256GB SSD+ 1TB HDD
Here are some pictures for your reference.
It seems to be saying that your drive is in the process of failing. Try doing a complete powering cycle (including AC power and (if removable) Battery disconnect). If the drive shows back up, I would immediately make a backup of the important files on it as it likely will fail again soon.
Hope this helps,