backsliding 
 
there are four important things to know about it - all four pretty important too - 
 
1) it's going to happen - growth is not constant, and there will be moments it stalls or backslides - finding what to do when low is its own skill to work on
2) it isn't the end of growth. You didn't fail. Picking yourself up again is what consistency is.
2.a) You probably have retained some growth but aren't noticing it, and what you have accomplished before is practice - it might be easier to learn again, or learning might open up to more deep understanding not noticed the first time. 
2.b) be careful - sometimes backsliding... is really hard to recover from... if so, find a new path to forge, as if a floor fell out and now you have to go around it.... 
2.c) Sometimes notice that what you were doing didn't fully work, and modifying the technique or taking a different approach is smarter
3) Beating yourself up will only sink you in. Look for what motivates you, not for excuses. At times it is fine to look for why, in order to prevent it again - but don't forget to just look for reasons to keep going, to re-motivate. Looking for excuses is searching for reasons to keep wallowing. Remember to acknowledge any negative emotions, behaviors, etc. - they are part of your experience. But don't moralize those... there's no need. Recognize what you don't want as something to avoid, recognize what you do want as something to pursue, this is all that is needed. You are not a bad person because you did [X] - but you do recognize [X] as something you don't want to repeat. 
4) Be careful - because what you accomplished before might not yet be repeatable. I will use an analogy to explain... Right now, some of my body has good strength, but lacks mobility. Other parts of my body has good mobility, but lacks the needed strength. As I do my yoga to restore my health - sometimes I am overambitious - strike a pose I can't hold, and it only stresses the strength tissues. Sometimes I over-apply my strength expecting the mobility to match it - but all I do is overextend. It is the same way with backsliding - we have lost what we could do, but still expect to be able to do it. This can cause "over-extensions" or "over-exertions" that get in the way of growth - or even cascade into more backsliding.