I had one of these spasms one time while putting up Christmas lights. While placing the lights along the sidewalk....my back went out and I was laid out. I was almost finished and people were driving by admiring the lights while I laid there waving.....true story. My wife wont let that one go.
Regardless of how much I exercise my lower back I will always get severe back spasms once or twice a year. Just lay on your stomach and keep icing your back off and on every 15 minutes. I'm also the type of person that hates taking medication, but muscle relaxers do the trick if you are in a lot of pain. Some people might recommend stretching, but don't push yourself too hard.
I guess it depends on the severity of the spasms.. I honestly couldnt lay any other way without being in a lot of pain.
Getting your tub as hot as you can stand it, with some soothing additions to the water, and then staying in it until the water gets cool helps me a lot, temporarily. I'll give you another suggestion, but it's not as much fun in the tub, relaxation wise, until you get out. Pour a pint of apple cider vinegar into the tub before soaking. It makes your muscles limp for awhile, which is groovy. The downer is the smell... shower it off. Good luck! Clearly, a hot tub is great, but you can't add too much to the water, or you have to change it... a real pain. I'll stop for now. I've has more back issues than I care to think about.
Just got home...I think I'm going to lay on a heating pad and stretch this sucker out. If nothing else, I may jump in the jacuzzi with some hot water and put the jets right on the spasms. It could be worse...I could be at work...
I'm guessing that it's late January and that one lone gosh darn strand is still up there, isn't it? A "While I'm up there... you want me to bring down the Christmas lights?" - G-Lo