If you want an independent view of Assange's mental health and wellbeing, you're going to have to wait. He is being held in Bellmarsh so that nobody can actually verify anything - not even his lawyers, and that IS THE POINT ENTIRELY - thus giving the CIA and its UK lackeys every opportunity to have their way with Assange, without anyone knowing anything until its well and truly, too late.
If you want 'independent verification' before you're willing to believe the state would do this to its enemies, maybe you should look at the long history of other enemies of the state being chemically lobotimized once they are held in secret conditions under the control of agents of the very military-industrial complex institutions whose crimes against humanity are being revealed.
BY DESIGN: there is no public oversight and there won't be until they have finished their lobotomy operation.
This is a serious situation which requires citizens such as yourself to have the courage to confront the details: the West has been torturing and disappearing its dissidents for decades. Go find out for yourself how bad it is.