After i woke up yesterday, suddenly i had really horrible backpain. i was perfectly normal till yesterday. what could it mean?

Muscle pain: The back pain can be caused by muscle strain, spinal stenosis, ruptured disc, nerve impingement ... It sounds like you might experience muscle pain from sleeping position. I recommend you trying heat pads, exercise, massage. If your pain is not improved with these treatment, please see a doctor for evaluation.

Acute LBP: Could be referred from your pelvis or urinary system if no history when you went to bed and then woke up with it.

Muscle spasm: Muscle spasm most likely should respond to nsaids, stretching, exercise, cold therapy. If persists may indicate some facet joint irritation.

Varies: Multiple potential causes, sometimes can be from an inflamed disc or facet joint in your back. Thankfully the natural history can often be favorable with quick resolution, but don't hesitate to be seen for it. Sometimes there are non musculoskeletal causes as well, such as a kidney stone for example.