Why do I always feel like this on day 2 and 3?

Anyone notice that they feel down and a bit shitty on day 2 and 3? I'm on day 3 now and I ALWAYS go through like a mini depression. Low motivation, can't lift as well in the gym and just feel lethargic. I know it'll get better, but anyone have any thoughts on this? Something to do with dopamine maybe?

 

Yeah it always comes back from day 4 onwards and I usually feel a lot better. These first couple of days I always start to think about things I've been repressing. People I'm angry with who have wronged me or situations that I can/can't change etc.