Ahsan Allahu Ilaykum. Is writing our tough emotions and painful stuff in a diary considered complaining to oneself if it is done with the intention of getting things out because of feeling emotionally overloaded and numb? Or does this only become complaining when one tells others?

Ustadh AbdulAziz al-Haqqan

It is not forbidden to journal, expressing yourself and state without objecting to Allah for example or something else that is forbidden. However, I advise you to seek out medical help as they have many ways to help in sha'a Allah.