Whites tree frog sick?

Hi

my whites tree frog has been acting very strange recently, his cage mate died a few weeks ago after escaping and ever since then hes been very lethargic not really doing any thing and spending a lot of time in his water.
now he is making movements as if he has hick ups and opens and closes his mouth form time to time. also his belly looks sort of yellow and his colour is half light green half dark. i have a link to a video of him to give you a better idea. any info would be great.

many thanks
jakk