Nauseas, feeling griddy. The problem is?

Hi, I want to consult about my Grandfather's ailment,five years ago he survived paralytic attack,after diagnosis it was found..the attack was due to blockage of an artery around the right side of his neck. Now around fifteen days ago some other health ailment popped up!! It all started with he's been feeling giddy..After some test been done thyroid(high TSA)was detected which however was normalised after some medical dose with he continuously feeling giddy all the time. Now he's feeling nauseas...with weakness playing its part all the time..no appetite for food,severely upset stomach. I just wanted to know..what exactly the problem is? No doctor is able to pinpoint the exact cause of his medical condition. I'll be highly obliged if any doctor could help us. Thank you!!!