That strained/restricted state is a familiar feeling to me Tammy. When everything is in tension it doesn't take much to develop those knots and spasms when you tweak things in the wrong way. A couple more points I forgot to mention above that are helpful in addressing such issues...
One is that it is very important to get the back moving in order to let the muscles adjust themselves to a less strained state - so a strategy of inactivity and pure rest is typically ineffective and counterproductive. Lifting, pushing and pulling when your back is like this is not a good idea. But short, gentle relaxing walks definitely are important if you can handle that. It's just amazing how much one's back muscles are gently exercised and get the chance to settle down by themselves, just by walking gently. However slow the pace, I find that can work wonders when my back is locked up.
The other thing I didn't mention before is the benefits I gained from my pre-existing knowledge of Tai Chi and Aikido. Having an understanding of the best (most mechanically efficient) ways to push and pull and lift can be really helpful, and some of the really basic exercises from Tai Chi can help a lot (though some are far too much of a strain and we need to do Tai Chi in a really gentle way...some teachers have a more 'yang' approach than others, and every teacher is different...). Those kind of exercises weren't the whole answer for me; I need the other factors I've mentioned above too, but effectively having some understanding of how to 'massage yourself' makes a big difference. Of course, a good massage from somebody else is still great too - and I'd particularly recommend Shiatsu as a great way to get a 'reset'. I've mentioned a few times how helpful Shiatsu was for me, and I do think it's really worth considering for people with ME/CFS. One of the great advantages is that the Shiatsu practitioner is effectively giving your whole body a kind of gentle, sensitive workout while you lie back and relax (and meditate if you like!). For people with PEM, who aren't able to be very active, but also therefore can have secondary issues caused by deconditioning, I think it can be a great way to keep your body moving without inducing PEM. It can also help to give you some awareness of those mechanical and balance factors that you get from Tai Chi etc, which is often too tough for many people with ME/CFS to do without getting PEM.