I worked as a Ward Manager in the NHS for thirty years caring for people with learning disabilities, it's probably lifting people out of beds and wheelchairs before lifting equipment became available. It will be fine but then something daft can set it off, it was bending down to switch off a socket that did it the last time and stepping over a ditch this time.
Thanks Tracey, it's a bit better today, sitting too long means it's sore to stand up and standing too long means it's sore trying to sit down. Lying downs fine but then I can't use the laptop. I've had it before and it takes a while to get better.