Evolutionary theory suggests that animals and humans co-create different role relationships (e.g. attachment, sexual, domination and subordination). Different role relationships are created through communication or signals, and different social signals activate different brain and physiological systems (e.g. affection signals can activate oxytocin, while aggressive signals activate stress-cortisol release.
Importantly, our response to externally or internally generated cues/stimuli is the same. Just as an external sexual image may stimulate arousal, so too can a mere fantasy that is generated by the individual internally.
This similarity in our responses regardless of whether they are generated externally or internally is important when we consider the thought–emotion processes involved in self-criticism. Self-criticisms serve as internal stimuli that act like social stimuli. And just as the brain responds to external criticism as a threat, it responds to self-criticism similarly.
So when you swamp yourself with a whole bunch of criticisms (e.g. you have failed again, you are no good, nobody will love you), your brain responds to these put downs as if they were put downs being told to you by someone else. And you respond just as you would if these attacks were delivered by somebody else (typically by feeling anxious, stressed or depressed).
These self-criticisms can be seen as a form of internal self-harassment, which can regularly stimulate submissive, anxious and depressive defences, especially if a person does not defend themselves against these attacks.
If you are finding that you are often criticising yourself and have been experiencing problems with anxiety, stress or depression, it is important that you seek professional help. Psychotherapy such as cognitive behavioural therapy (CBT) can really make a difference in helping you to overcome these issues.