Dropping 4 lbs in 24 hours

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That's got your attention I bet. Has anyone else had this amount of water retention due to a spinal arthritis flare up and taking the maximum dose of ibuprofen plus solpadol? I was a bit annoyed yesterday morning that I had appeared to have put on 4lbs but my back is improved, I stopped taking so much medication and this morning it had all gone. Is it the inflammation or the drugs? (it's not my scales - I can assure you it was water retention as I spent half the night peeing)