I read a lot here about the later stages of psp and it breaks my heart. I think some of the rigidity/pain issues and night terrors/anxiety can be eased (to an extent) by using cbd oil. It's non psychoactive, its legal and you can buy it in the UK. It's also been proven effective in reducing tremors in Parkinson's patients.
This is the recent release from clear UK in April 2015. They are the organisation heading the legalise cannabis campaign in Britain. Please don't let that last sentence close your mind to this medicine. The evidence is too great to dismiss.