Have you ever stubbed your finger ?
Your finger swells up and you can’t move it.
Then the swelling goes down, and all is well.
Most likely, you “stubbed your back” and there is swelling around a back joint which is pinching a nerve.
Hopefully, the swelling will go down and every thing will be ok.
Oh when you stub your finger, it is best not to move it.
Ditto for your back which will be more challenging not to mover for a few days.
I remember the first time I strained/sprained my lower back. It was sore and stiffened up through the evening, but in the morning I literally couldn’t get up.
I ended up rolling out of bed onto the floor and then took a half hour to inch my way over to where I’d left my cell. Called a friend and by the time he got there I was a little better, so he didn’t take me to the ER. Then it was about 30% better day by day over a couple of weeks until it was gone.
Don’t remember but think I went in to see a doctor within a couple of days, who told me it was a sprain and to rest and take Ibuprofen and then only gradual stretching and strengthening. Don’t think I even went in for PT. I’d sprained ankles a few times, so I knew the drill.