Imagine a 4/4 beat, imagine the beat sounding hard, shallow and cold (a thud rather than a boom) with no warmth and no depth to it, now imagine the beat giving you a slight headache, imagine thinking to yourself "Do I have any ibuprofen or aspirin the house?", imagine discovering you don't and consequently having to lie down on the couch with cold teabags over your eyes for half an hour. That pretty much sums up the majority of full-on.
Hope that helped.