If you could sue an airline just because you hurt your back inflight I think we’d have seen a whole lot more lawsuits since the introduction of ‘slimline’ seats that have less padding, and so take up less space, and allow airlines to squeeze seats in closer together.
One man though says he hurt his back when his United flight diverted to Goose Bay, Canada in October and he’s been having “horrible plane crash nightmares” ever since.