Him feeling okay scares me, makes me feel like he could forget all the pain he felt and caused.
ThisIsSoFine nailed it.
This is about your trauma and what I call the lizard brain (really a bunch of parts of our neuro system) will fight really hard to have you on 'high alert'. You lizard brain is doing all it can to make sure you don't forget that pain (think about it - we're talking the same parts of our nervous system that kept the cavemen alive... if their buddy gets eaten by a tiger, they need to be damn wary next time they see a tiger, or there is no human race).
If you are interested, in addition to How to Help Your Spouse Heal From Your Affair (which I'm told you can find online for free -and am curious if you read it after your 1st dday), I'd check out the 2-part interview of Marnie Breecker on Duane Osterlind's "the addicted mind" podcast. There is a thread about it on SI that I think I can bump, but you should be able to find it online. It's about 60-90 minutes total. It basically talks about the ways in which a BS is traumatized by relational betrayal trauma. It helped me to understand that my inability to "snap out of it" wasn't me being crazy, but was a trauma response. Breecker & Osterlind went on to create the Helping Couples Heal podcast, which helped me tons.
To understand trauma, the "bible" on that front is "The Body Keeps the Score" by Bassel Van der Kolk. It's a LONG book, with history, the politics of the DSM, etc. AND it presents a lot of research and understanding on trauma, how it impacts us, various modalities for treatment, etc. I found it fascinating as a regular "person" and as a BS, but it may not be for everyone. It has nothing to do with infidelity.
As to this next one, I want to start by saying that while it's not in the cards for me personally, I still ABSOLUTELY believe that R is possible, that BS and WS can heal and grow and forge a new M via R (even after a 2nd dday). Anyhow, there is a book ("Cheating in a Nutshell") that does connect the dots of trauma/PTSD and infidelity. HOWEVER, I believe (as do many others) it has a decidedly anti-R bent, even tho I also think the info is accurate. It basically presents a bunch of studies about trauma against the backdrop of infidelity. If you have any interest, I would start with the thread about this particular book in "the Book Club" forum on SI. Despite my disclaimers, I found the book to be a good synthesis of what's happening in a BS' BRAIN in the aftermath of infidelity/dday. That perspective is helpful for my particular personality, but maybe not so much for others. I honestly think that it should be required reading for WS.
Along the lines of shame - reading that your pain is making your WS physically ill is, IMO, a HIM problem. IOW, he is making YOUR pain, that HE caused, about HIMSELF. That is not empathetic. It's not remorse. It's HIS shame taking over. (and at dday2, it's disconcerting to me). You may want to explore the dynamic of you feeling better by comforting him. NOT saying there is something "wrong" with it ... I AM saying that your energies may be better focused on comforting yourself, self soothing, etc.
Finally, given this is your 2nd dday - what did you/WH do to R after the last rodeo? Did he do IC? What factors or changes led you to commit to R last time?