Stage 4 is generally considered the second most technically difficult Stage. Only Stage 8 is harder.
There are several reasons for this. Not all Stages are the same “length” or difficulty. Stage 4 is “longer”, in that there is more to accomplish. It is also more difficult, in that each minute of meditation seems to accomplish very little. The meditation itself can feel quite delicate. It can feel like you are trying to do brain surgery while being driven down a bumpy road with a marching band playing in your car.
Then there are the purifications. An innocuous sounding sentence in Stage 4 (p 139) says, “The emotional purification in Stage 4 can be the equivalent of years of therapy”. What that means is that Stage 4 loosens up long suppressed and undealt-with issues. They will bubble to the surface. For me they appeared as an old issue/memory “tapping” on my awareness and going “remember me? It’s time”. The best strategy with purifications to be open, accept them, embrace them, and inquire gently what they need to tell you. Don’t dismiss them. A single issue can cause weeks of sobbing as you process whatever it was.
If you ever think you can’t handle what comes up, consult a professional. Also consult a professional if you just want some help coping with everything.
Some people don’t have anything come up in Stage 4, others have quite a bit. You will be a better, healthier person when the purifications finish, but it can quite a bumpy ride.
I consider the purifications to a parallel track to the stated goals of Stage 4, and I think they are more important than the practice. I think it’s fine to pause your practice if you need to in order to deal with the purifications.
In Stage 4, sometimes your mood (Your Mood is Critical) matters the most. If you are prone to distraction (involuntarily switching attention away from the meditation object), being extra careful about setting a happy mood before meditating is critical. Physical exercise right before meditation can also help – it usually tires the system a little bit, and the “well-being” feeling after exercise helps stabilize attention.
If you are prone to dullness (Quality of Peripheral Awareness / Dullness) this Stage can feel impossible. You have an extra task – which is recognizing the signs of impending dullness and intervening immediately. Working with dullness can feel you you are doing a different practice, and in a sense you are, but leaving dullness unchecked will absolutely preclude progress. The good thing is that as impossible as dullness seems, it is completely doable to train yourself out of it. It is just slow and steady work, like the rest of TMI.