Welcome to SDMB, @pacheen1!
I got Pfizer and arm was a little sore #1, then #2 was sore and I was tired for a few hours.
Mrs. L got Moderna. #1 arm was a little sore, #2 was fine for about 12 hours, then her arm got really sore, she had swelling, and she needed painkillers. About 24 hours after the second stab, she’s starting to recover.
They say her reaction shows it’s working. What does my (lack of much) reaction show?
That it is working.
First dose scheduled tomorrow. They claim it’ll be Moderna.
Got 2nd dose this morning. Felt great afterward, so decided to go for a long walk. I got very fatigued and moved like molasses. I almost ordered Uber to get home. I now have chills and a low-grade fever. It’s really not too bad.
Got socked by the second dose, as expected. The reaction began at 2 am, 12 hours post the second dose. Severe body pain, probably a low-grade fever. Muscle cramps in the legs. After 24 hours I am much better, though not totally OK. I hope the worst is over already.
I have read that people who have actually had COVID-19 had a worse reaction even to the first dose. I thus have an educated guess of why the second shot is worse and why some have it worse than others:
Any exposure to the spike protein results in your body building up some specialized immunity. If you’ve already had the virus, then it will be primed to go after the spike proteins, which will invoke the rest of the immune system, causing symptoms. Similarly, if you were primed by the first shot, then it will do so for the second.
If you have a strong reaction, that would suggest to me that you developed some stronger immunity in your first exposure than those with a weaker reaction.
Of course, there are other variables. For example, it seems that older people are less likely to have a stronger reaction, if I heard correctly. So I’m not saying this alone is a factor. But it at least is something that makes sense to me.
And it’s also why I wonder if the eventual third dose is more likely to be worse, at least, in a single person.
Still, there are those who seem to have less reaction the second time, too. My dad is one of them, so I’m hoping that extends to me, too. But it could just be his age.
People who are immuno-suppressed reportedly tend to have milder reactions as well.
That’s the common trope but I wonder if it’s really true. There are so many other variables. I’m far from an expert in this field obviously but sometimes I feel like it’s something said to make people with strong reactions feel better. I don’t think that people with no reaction are less protected against the virus but time will tell.
I’m getting my second on Monday morning. Here’s hoping for the best for all of us.
When I woke up the morning after shot two, I was really tired and a bit achy all over. Fed the kidlet, took two advils and had a medicinal gummy bear. Couldn’t get out of bed all day. Day two, had teh same breakfast but much less sleepy. Day three right as rain
I get my 2nd shot Wednesday morning.
I have two immuno-suppressed family members. Neither had any noticeable reaction to their immunizations.
I got my second dose of Pfizer on Thursday. By the end of Thursday my arm was a little sore. Friday my arm was sore enough that I didn’t want to raise it, and I was tired enough that I took a long nap in the afternoon. Oh, and all my ordinary aches and pains seemed worse than usual, although it’s hard to pin that directly to the vaccine. Today I feel fine. A little bit of arm pain if I poke at it, but nothing I’d notice otherwise.
I’m in my late 50s, and tend to catch colds. But other than that, my immune system seems fairly normal.
The wife got her second Pfizer dose on Thursday afternoon. Felt a little achy the rest of the day, but that was it.
Quoting myself for context …
Aaand … I got my wish.
Got my second Moderna on Fri midafternoon.
6+ hours later I’m prepping for bed and have that “I’m starting to catch a cold” feeling. Slightly achy all over and unreasonably lethargic.
Slept poorly and was slightly chilly all night; should’ve gotten up and added a t-shirt but didn’t want to get out of bed and get even colder. It’s 77F in our bedroom, so hardly frigid. Had a couple of involuntary shivers, but far less than having a real fever.
Problem peaked at about 12 hours post-vax (IOW in the wee hours) and by now, almost 20 hours post-vax I feel very slightly stiff and a bit draggy; not too different from just before bedtime last night. I took my temperature when I first got up and it might have been up 1 to 1.5 degrees. Except for the muscle stiffness this now feels more like the aftermath of a bad sleep than an illness. No issues with local discomfort or range of motion in the vaccinated arm; it’s the same as the other one.
I did do acetaminophen every 6h from right after the vax to now and will probably continue that until I feel normal. And I’m pushing water even more than my usual “lots”.
All in all, I call this adventure a success.
My first dose was April 17. Spent a few days unreasonably tired and had one day of unhappy lower digestive system. My arm was a little tender, warm, and slightly swollen around the injection site for a couple of days.
Second dose is May 15. We shall see. Moderna in both cases.
I got my second Moderna shot recently. I was dreading it, but it’s not much worse than the first one. I had arm pain and a headache, some fatigue too. but nothing terrible.
And let me guess . . . You were scheduled for a trans-continental flight at 6:00 a.m. the next morning. 
Actually, by FAA edict we are required to take vaccine day and the next 2 calendar days off. Since my vaccine day was known well in advance my monthly schedule was aware of this requirement. This is the first weekend I’ve not worked in the last couple of months. A nice respite and well worth the funky overnight I went through.
Following up on my symptom report above it’s now 29 hours since the second shot and I feel normal. Assuming I sleep well tonight there would be no practical obstacle to me working tomorrow. Though the FAA will not be denied or defied. 
I’m wondering about the third (booster) dose. Mrs. L had a bad reaction to shot #2, said she would likely skip the booster if it were required. I had no problems with shot #2. She had Moderna and I had Pfizer…will they allow a switch if a booster is needed?
Nobody knows yet. AFAIK, today boosters are a theoretical possibility and nothing more. As well we may be getting updated vaccines every year like we do for flu as this virus keeps mutating in the hundreds of millions of infected people around the world. Or maybe not.