No it's not in your head, the pain is real! What they mean I think is that when pain lasts too long, the brain starts over-reacting to it and makes the pain feel even worse. It gets over-sensitized and sends pain signals when there isn't any danger to your body occurring; and things like stress, anxiety, worry, fatigue, makes this even worse.
Chronic pain is absolutely horrible. I have it and there are days when I could scream.... but I know they settle down and I go back to being pretty OK. I really understand how much you must suffer from it, I remember telling my doctor I didn't know how to survive through it at times - but the stretching/meditation/heat packs/exercise has made it much more manageable. I still wish like heck I didn't have it, but I can manage it more or less OK...
I had a steroid injection into the spine and it helped slightly for a few weeks, that's about all . I was really hoping it would give complete relief but nope! So then I concentrated on yoga stretches, heat, relaxation, careful exercise, and laughing at funny things actually is really helpful!
I think people who suffer from chronic pain are incredibly brave - people who don't have it just don't understand how exhausting and debilitating it can be. I really hope you find something to give you some bit of relief!!! I find it frustrating that people think I've just got a bit of back ache and suggest I use a couple of cushions when I sit down - it's nerve pain from the disc pressing on the spinal cord and it's like being boiled alive, but people just don't get that!!!
Really here to give you support when needed my friend!