For the freestyle, make sure you do not rotate your head too much when taking breaths. In addition, do not let your head move up too much or deviate from the axis along the length of the body. Deviating from this axis, or over rotating the head, can easily lead to neck and back injury while swimming. Also, when you’re not going up for breathes make sure you keep your head looking downwards. As already mentioned, rolling too much can easily lead to damage.
With the backstroke, muscles along the front of the neck tend to become fatigued if you have not done that stoke in a long time. Make sure to ease into this stoke and avoid over doing it.
Be careful as back injuries may ruin your swimming career.