to cauliflower1. Help is at hand for this horrible (but beautiful) passage.
Firstly, the sixths. The big distances between the two notes of each sixth might cause too much stretching, which will make your wrist stiff. Practise these bars REALLY slowly, breaking the bars into bits. Make little repetitions of the bits. Make sure you are not 'bearing down' on the keys and that you are practising cautiously. As you speed up the short bits, and then longer bits, play even more lightly.
Good luck. I will return tomorrow with my ideas about trills. (Don't attempt to practise the two horrors together.)
When you can play this passage as Chopin intended you will sing with delight.