Working with cycles in meditation

Over the course of my meditation practice I experience pronounced cycles or ebbs and flows. This has been a feature of my practice for several years now and doesn't seem to be lessening - if anything it is intensifying. The pattern is 1. Meditation goes well. Concentrated and experience vigour 2. Energy, motivation and concentration increase to a peak 3. Over the course of one or two days practice seems to fall apart. Poor concentration. Feelings of dullness and lethargy with meditation and lack of motivation. This can bleed over to time off the cushion 4. After weeks or even months meditation starts to become pleasurable again and the cycle starts again Sometimes the low point isn't too bad but sometimes it is so dominating that I can't recognize it for what it is. I've cleared my shrine away before now. The Buddha goes away and it's only after some days I remember what is probably going on. Does anyone have any advice about the best way to work with these kind of cycles. Is it a well documented phenomena or documented at all? I would find references to established texts or teachers on this subject particularly helpful.