As you're probably already aware the bloating & breathlessness are probably due to fluid retention. 3kg weight gain overnight is a lot of gain which again indicates fluid.
You do need to let your medical team know this is happening as you may need your meds tweaking. Also you may need to have bloods taken to check your kidney function as furosemide can affect your kidneys.
Good luck, I hope you get it sorted quickly but if in doubt, always phone nhs111 for advice, fluid retention can be quite serious.
My lowest weight would be first thing in the morning before breakfast or a drink. The highest last thing at night . I would expect the difference in readings to be around 1kg. Then that would come off again by first thing next morning..
Would be interesting hear of other peoples weight fluctuation to know what is considered normal..
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