I know an ENFJ who does that from time to time. I know she'll spring back soon though, so I let her be. I've realized that I just can't push her when she's in "that state."
It does worry me when she starts to say "dark" things (like "no one really cares (about me") though.
Ah, well. Everyone needs to "re-charge" from time to time I think. All I can do is to support her through the had times. She does express gratitude to me for being there for her, so it's all good.