Hello and thank you for bringing your concerns to Just Answer...and can truly imagine your concerns with this..
To perfectly honest with you to rock back and forwards is done by way of a repetative motion for many to 'self comfort' when feeling, tense, anxious, tired, bored, lonely up tight, even depressed or sad
In otherwords this is a comfort action where for you it creates a great sense of pleasure and relief..whereby you feel at ease in yourself and your own skin..
My own son does this and it is a learned comforting behaviour..
Though, for some it may or may not become a compulsive addictive behaviour.for others it simply is a release to help one 'tune out' and feel free in ones body..
I honestly don't suspect that there is anything to worry about..my son was assessed and was told the same thing..To some children its a bit like carrying thier blankie'around with them..Though of course as one moves on into early adulthood and or adulthood you naturally leave your comfort blankie behind..and for others comfort is sought through a gental rocking motion similar to that of being found in the mothers womb..
I truly hope that this has helped to put any fears or concerns aside...because it certainly beats self medicating and or seeking comfort in a self defeating way...which many sadly seem to choose to day..
Take very good 'self' care now and continue to 'touch base with self in this way because it also helps to create a greater inner awareness..
p.s and I truly apologise for any late response that may have resulted as it has much to do with world time difference I'm afraid and when an expert is next available to answer..