Can a irrevocable trust be contested?

my brother was very grave with liver cancer,and the doctors only gave him a couple of days to live. he went into the hospital on nov.2,2007 and by nov.5,2007 he was put into the hospic ward,where on nov.11,2007 he died. on nov.5,2007 his attorney came in his room with a will and trust for him to sign. my brother didnt even know what day it was or who the presentdent of the u.s. was.itold the lawyer not to let him sign anything because he was on a double dose of morphine.but his lawyer had him to sign the trust anyway being under the double dose of morphine.the trust was sign on nov.5,2007 the same day that he was put in the hospic ward and he died on the nov 11,2007.do you think the irrevocable trust can be turn around,because my brother did not read what he sign or could not understand at that time what he was signing,because he was on a double dose of morphine and than when he got to the hospic ward they put him on hydrochlophine which is stronger than the double dose of morphine,and the doctor gave him an i.v drops every 10 min. so can you tell me if this irrevocable can be contested?