Hi Neriz, to me this sounds like 'dissociation' or 'splitting', which is a defence mechanism that kicks in to protect you emotionally.
Like blocking off the feelings about your mum or not remembering stuff from the summer.
We are all capable of doing it, to a greater or lesser degree. It protects you from feeling and/or remembering painful things.

It sounds like you are aware of when you choose to do it, but not being able to remember the summer could have been a time when it happened unconsciously.

Do you have a counsellor or therapist Neriz ? It would be a good thing to talk to them about if you do. In my humble opinion, there is nothing wrong with it unless it causes upset to your life - if it gets you through, then, hey, you have that 'up your sleeve'

Care, Poppet