Hello Dear. I m not sure of your age. If you are a young person i may think of just simple causes like dehydration. Dark urine may be just due to dehydration. If you are an elderly person i will think of more serious causes. When you are saying that you have retention of water in your ankles and feet and feeling nausea, then it points towards kidney pathology. Kindly go to the physician who will do blood test and urine test. Renal function tests in blood will reveal if there is elevated urea and creatinine in blood which points towards kidney damage. Long term medications and if necessary dialysis will be done. But as per your limited history it is difficult to arrive at any conclusion. But i suggested you to kindly consult a physician at the earliest and get a detailed evaluation. Hope i have answered your question. Feel free to contact me if you have any more questions. I ll be glad to help you. All the best With warm regards Dr Sanjay Kini