What to do for a thrown back?

Basically, I have had some stress on my back in the last 72 hours, moving things i had to move, etc...

and yesterday, in the middle of a seemingly harmless motion of lifting a book while bending over, all of the muscles in my lower back just *seized* and I could do little from falling over.

as long as I lie flat on my back on the floor it's bearable. when I'm sitting up it's very painful and if I bend at all it's excruciating.

I took ibuprofin and this morning I put an 8 hour heat pack on the back.

the way i would describe the pain is --- imagine a contortion-spring scorpion or crossbow --- where the string winding up on both sides of the bolt provides maximum pressure... that's the picture i have in my head of all of the muscles on the two sides of my spine.

lower back...

so, today is supposed to be moving day -- all my stuff's in the car and i'm supposed to get on the road to drive 2,000 miles across the country...what can I do to help heal this situation and loosen those muscles