what to do, when you can't meditate?

I am meditating on a daily basis since a couple of months. I noticed having ups and downs in my meditation, probably mostly caused by the amount of sati or (on the other side) stress I had during the day. But I am also experiencing sittings, where I am just overwhelmed by the hindrances and not even able to recognize them properly. What is the best way to deal with these extreme states of mind (in meditation)?