at death's door	jedna noga na drugim swiecie
there's a bug going around	zarazki lataja w powietrzu
give sb a clean bill of health	dac komus swiadectwo zdrowia
go down with sth	zapasc na chorobe
in good shape	w dobrej formie
my back was killing me	bol plecow byl nie do zniesienia
under the weather	niezdrow, niewyrazny