You have my sympathies, my 12 month old is the same, she used to be fabulous and would just nod off but for the last week or so she has YELLED when I put her down, unless I snuggle up beside her for a while. It is all rather difficult. She too has been ill, but is now better. It seems that she just wants me to be close.
I have no answers I'm afraid and will be interested to see if anything comes up. In the meantime I am making sure she is well fed, sleepy (but not over-tired), clean bum etc. Then I comfort her a bit and try and put her down, leaving until I can stand the yelling no more (usually 10 mins) then trying to calm/settle again.
I wonder if separation anxiety kicks in more strongly at this age?