The only time you should feel bad about taking a break, meaning going into child’s pose or dead man’s pose during the middle of a sequence, is if you are doing it because you are feeling lazy but rationalizing doing it as because you are feeling tired.
Otherwise you should feel good about taking a break, whether it’s because you’re on your edge and pushing it hard enough that you really do need a minute to regain control over your Ujjayi breathing, or because you simply are feeling lazy and know it, refusing to entertain any illusions about your state.
The first is probably better for propelling your asanas forward but both are good for propelling your yoga practice forward because both do away with ego rationalizations, the ones that either tell you to keep going even though you need to take a break or the ones that tell you to quit even though you could easily keep going.
Yoga, just like psychoanalysis, is concerned with eradicating all ego rationalizations. The philosophy of yoga, like all good philosophies, is concerned with truth and the search for it. You will never be on the path of truth as long as your ego is in control rather than that deeper layer of Self.
Especially when you’re on your back because you’ve just worked really hard and need a moment to recompose, feel really good about that, about not just your effort but also your conscious, mindful awareness of what you and your body need at that specific moment. On the yogic path of mindfulness, knowing when to pull back is every bit as important as knowing when to charge forward. Walking that line is what will propel your personal practice forward fastest.