Do not just lie in bed, forget your worries, try to relax and sleep. The idea is always to take some care, since sleep directly affects how your next day will be. And when it comes to sleeping care, the pillow plays an important role.
Taking into account that the spine should always stay straight, sleeping without pillow can do harm or not, it depends on the position you usually sleep. For example, if you sleep on your side, sleeping without a pillow is not a good option since your head will stay ‘hanging,’ damaging your spine. For sleeping on the side, using a pillow that leaves your spine in line is the best option.
They say that the best sleeping position is on your back, straight, on a surface not too soft, in this case sleeping without a pillow would not cause any problems for the spine and even help in case of back pain. I have heard many doctors recommend this position and also without apillow.
Dr. Andrew Weil says that the pillow is a matter of personal comfort, while some sleep peacefully without a pillow (not sideways) others need more than one pillow because of reflux. The only recommendation he makes is to choose a pillow that does not store heat since we need to lower the body temperature to sleep well, the goose down pillows perform well for example.
For babies, first of all, they did not ask you for a pillow to sleep, it is natural for them to sleep without a pillow. Secondly, pediatricians do not usually indicate pillows because of the formation of the spine and the shape of the head. And in case you prefer to put a pillow for your baby to sleep, use a thin crust.
Conclusion: At first sleep without a pillow has no problem, as long as it is not sideways. There are many people online who report relieving pain when they sleep without a pillow. I always sleep without a pillow; I do not have any pain or discomfort, I just keep the pillow in bed in case I read a book.