In that sort of state, your refuge is observation (stop thinking; just be aware) because the mind is already in a downward spiral; anything that the mind thinks, it’s going to be wrong for the mind.

At that time, what you do is just observe. Stop thinking about it; rather, how does the body and mind feel? It feels not good; it’s not comfortable. Keep watching all that as long as you can.

What you’re experiencing is doubt – it’s just a defilement, a hindrance. The way to deal with it is to observe it. You make the hindrance the object, and it becomes part of the practice. And you have to observe it until it’s not there. It’s an object that is very available; and until it clears, don’t think about it.

Don’t decide anything about your practice; don’t make conclusions or judgments because the mind isn’t thinking in the right way. Put it aside and stay with the simple feeling.

Use it as an object – see what it feels like and the effects it has on you. You can also go back and forth to the body too. 
At that time, make the mechanical type of awareness where you keep making sure that you’re applying awareness your goal.

You can also try looking at doubt directly; and sometimes the mind finds its way and it can watch it, and then doubt disappears. And when you’re struggling with that, go back to the body and feelings which are more immediate and more available.