It's a real thing. And it's terrible.
The first time I felt mommy guilt was when Elsie was only a couple of weeks old. It hit me hard because I felt super guilty for giving up breastfeeding so early on when I started going to baby play dates and saw all the other mommy's breastfeeding. I felt like I gave up to early when I should have tried harder, that I was letting Elsie down, and letting myself down as a mother. I struggled with this feeling for months as I felt like I constantly saw women breastfeeding their babies. I worried about if my bond with Elsie was as strong as it should be, that she was getting enough nourishment and antibodies. Eventually I realized that Elsie was doing great as a formula fed baby! We had just taken a different path, and that was okay. She has always thrived on formula and though it was rough for me, it wasn't necessarily a bad choice choice for her.
While that was the biggest bout of mommy guilt I've felt, there have certainly been other times. Anytime Elsie has bumped her head or fallen while trying to stand, I'll think "crap I should have been there to catch her instead of whatever else I was doing!". When I gave up cloth diapering, baby led weaning, etc. "Am I making the right choice?" Anytime she's gotten sick, "was it because I didn't sanitize the high chair, or didn't put her coat on, or didn't wash my hands enough", etc. etc. etc.
The reality is that it can be really tough being a new mom and having so much responsibility over another human being. Not having done anything like this before and having to navigate the roads of new motherhood or even repeat motherhood (for lack of a better word). It is a challenge! But we have to give ourselves a little break once in awhile and take a deep breath. Our babies are alive and thriving! All babies eat and grow no matter if they are breastfed, formula fed, fed with purees or using baby led weaning. They all occasionally bump their heads, get bruises, and get sick. As long as we are doing our best, feeding and clothing our children, we are doing enough.
So you, new mom, seasoned mom, give yourself a break and a pat on the back (or a glass of wine) and know that you and baby are doing great, even (and especially) on the rough days!