Everyone experiences ebbs and flows, it is the natural biological cycle of the mind. However its impact varies from individual to individual, and can definitely be controlled.
First, we need a good reason to continue practicing when meditation loses its stickiness. Second, we need to intervene early, before the multiplier effect sets in. If the dullness (which is what doubt is) of mind lasts for too long, then stronger and still stronger medicine becomes necessary, and it can be quite painful.
If we are in a retreat setting where our attention and mindfulness are excellent, we can spot the exact moment the mind changes its hum. Doubt begins to creep in, and a lack of confidence, or a desire for samsara grabs one. At these times, provided this change is noticed at the very first moment of arising, it maybe sufficient to just note the change, and it will vanish soon without much harm because our mind will multiply it no further.
Usually for me this would happen on some days at around 3-4pm when I'm having a calorie crunch, being 4-5 hours after lunch, my mind is switching fuels, and has a lower performance initially when burning fat reserves.
Fewer calories coming into the brain = Depression, despondence, laziness etc.
Of course, I can't observe at this level of detail in everyday life, so this only works for me on a retreat or if I am already on the cushion when this happens.
Next best case:
Take the philosophical approach, and ask, 'who is losing faith?', 'what is reality?' etc. Again, this works only if the intervention is quite early in the phase, when the mind still has enough strength to be reasoned with. Maybe within a few minutes of the dullness arising.
Medium - to - Hard cases:
Once the mind has become properly dull by lack of mindfulness, which takes only a few minutes (less than half hour) really, it becomes difficult to reason with. Moods and opinions take root rather firmly, and one may want to get up from meditation if one is already in meditation, or take a break from reading a book on dhamma etc.
If the lack of mindfulness lasts for a little longer, like an hour, then the mind becomes a proper bucking bronco. It wants pleasures, it wants a movie, it wants distraction, the works. It may want to leave the retreat right away etc.
If we let the dullness persist for a day or two or a week, or more, then yeah, giving up the practice all together becomes a real possibility. There are people who abandon meditation for years because they got dragged away by dullness, and then got caught in daily life.
The only option that works on a dull mind that is not sharp enough to reason with is faith and perseverance.
One time when I'd let my mindfulness slip on a retreat (in this particular case it wasn't lack of calories, it was the dukkha nanas), all of a sudden I had thoughts of quitting the retreat. It wasn't my first retreat, so I knew this isn't normal, this isn't right. I had no choice but to walk around in my room, cursing Mara, telling him he won't have his way, he is not going to weaken my resolve. I was simultaneously aware that I was talking to myself like one of those people in cults blaming the devil for everything, but what could I do, my mind was too dull for anything more rational or intelligent. The dull mind can't reflect within and see nuanced internal reality, so blaming the devil is what worked.
It brought me back to the cushion within an hour, because I was quite angry with Mara and wasn't going to let him win. The mood had passed by the evening. All one needs is some convincing reason to continue to practice - devil, biology, philosophy - whatever resonates at that moment. The good thing about blaming the devil is it fights depression and self blame - I don't indulge in the '"I" screwed up' thinking and get demotivated, instead fury at being wronged by Mara gives strength to fight back.
Off the retreat setting, there's been a few times, when I've abandoned all practice for 3-4 days, maybe a week, and binge watched some nonsense TV series or the other usually with a lot of stomach churning violence and sex. All the while knowing I don't really enjoy it, but I'll feel powerless. Of course in these cases I didn't catch the dullness early enough, and allowed it to multiply in strength. Once the mind is properly dull, it looks outside for entertainment. Sex and violence is popular in our present day culture because it is the lowest grade of entertainment - even the dullest mind can appreciate it even though it renders one even weaker. When my mindfulness is quite high I am repulsed by the sight of such things, and my mind will naturally stay away with no effort.
This situation is quite bad, because even after I've decided to pull myself up, which I usually do after a week maximum, I have to make up lost ground, and my concentration won't get back to normal for a week or two, and the whole time my mood and relaxation won't be so good. I might wake up a little extra tired, I might sleep late and wake up late etc.
Some other times I've just zapped out of the dullness as if by magic, and got back on the cushion after watching 3 seasons of a TV show back to back, as if nothing happened, and my concentration has not suffered much. This I can't explain.
My problem these days is complacency: I know how all this works, and I know I will eventually always return to the cushion, so I no longer fight it as vehemently as I used to. I'm trying to fix this but I can tell I am taking it easy.