Sorry you are not feeling well today:( I don't know if this is helpful or not but I've gone through similar in the past year and a half of NB. Sometimes I find it's as a result of doing too much and I just need to rest. But sometimes I find that my body is detoxing and I feel a little better than I did before when it's all over. It's kind of like two steps forward, and then you feel like you've taken ten steps back, but in reality you've taken another step forward when you come out of it...if that makes any sense.
But I know what you mean. You feel like it's impossible that you could go back to feeling this bad again and then Boom! you do. I think it will pass shortly though.
Hope you will feel a little better tomorrow.Keep us posted:)