Extreme senses/sensitivity to stimuli

So, divorce from my ex with untreated ADHD is almost final, after leaving with kids a year ago. Working on co-parenting, which usually consists of me managing and taking care of everything and him contributing what he can when he can. Which is actually fine. We get along reasonably well and the kids are happy. 

I continue to unravel the past and figure things out--hindsight is always good when we learn from it, right? And this one aspect of his behavior keeps rearing its head. I would like to be able to understand it and explain it to my children. For now I just ignore it--it used to drive me crazy and embarrass me, but now I just find it curious. Has anyone else experience this? 

My ex spouse definitely has ADHD, and maybe a few other things going on--bipolar disorder, depression, OCD, asperger's? I don't know. But he responds extremely strongly to various stimuli. For example, bad smells may make most of us cover our mouths, but he starts gagging, tears roll down his cheeks, and he makes loud retching noises. Everything from a dirty diaper to bad garbage made him do this (convenient, huh?) He once swallowed some food the wrong way and ended up rolling around and thrashing in the floor, clutching his throat. A friend saw it and asked if we should call 911. "No, he just does that," I answered. It is just really melodramatic and beyond attention-seeking. It is like there is something mentally wrong, maybe ill about it. Several friends and family members have asked me if this is for real? Small injury to his knee? Limping around with a cane and getting a handicapped tag for his car. He also looks up the worst thing that could possibly happen, medically, for everything and sometimes scares our kids with it. (Surgery for a pinched nerve? Could result in paralysis and he will never walk again). 

It is worst when he is in pain or sick. A cold leaves him making the most crazy retching and coughing noises, again with tears running down his cheeks. It is a bit annoying when I am trying to pay attention to our kids or he is canceling out of an overnight with them at the last minute. 

There has to be some explanation for this. Honestly, I don't think it's for attention. I think there is something that makes him over-react like crazy to things like this. And forget talking about it. I tried a few times and he freaked out and said I was accusing him of lying. Worst fights ever. Once I rolled my eyes at him (which is not very nice, I admit, but I had just had a Cesarean and was up all night and breastfeeding and couldn't take it any more). Well, I was the meanest human being who has ever lived. He absolutely freaks out if someone calls his credibility into question. 

So, I just let it go, and try to ignore it now, but it happened again this morning and I know the kids are going to start asking about it at some point. Any ideas?
Thanks, everyone. 

I'm non-ADHD (I think!) but I

I'm non-ADHD (I think!) but I have very acute senses of smell and hearing.  I can hear my husband chewing or scratching when he's in the bedroom and I'm in the living room, and I can smell food that's off much sooner or more easily than other members of the family do.  Unlike your ex, I tend to keep my reactions to myself.  Perhaps your ex's strong outward reaction is related to the ADHD:  less self-awareness of how his behavior appears to people nearby.  

My husband has ADD, our son

My husband has ADD, our son (5 years old), has anxiety and sensory processing disorder (SPD).  It's when someone reacts to stimuli differently.  Used to be called sensory integration disorder and a lot of kids on the Autism spectrum (including Asperger's) have this too.  Experts are trying to get SPD as its own diagnosis.  I think it involves Dopamine like ADHD, autism, tourette's, OCD, anxiety.  These are all other disorders that I have read about when reading about SPD for my son (I know that's depressing).  It's like a constant state of flight or fright.  My son would freeze and withdraw into himself when overwhelmed by stimuli (and sometimes you just don't know what that stimuli might be).  Some kids lash out.  New situations are hard because they don't know what to expect and what stimuli they may encounter.  My son is extremely sensitive to stimuli.  Holds his nose when something smells bad.  Would have a tantrum when the fire alarm went off at preschool.  Cried when someone accidentally bumped into him (it really truly  hurt him even though it was just a brush).  He is much better now so I can't give too many more examples.  Oh-he will only wear 100% cotton knit/jersey clothing, t-shirts and pants (not fleece pants or cotton twill).  He wears this all year.  will not wear long sleeves in the winter and will not wear shorts in the summer.  Wears only wear one type of sock (that only one store sells!).  Won't sleep with a blanket, even in the winter, and he is not cold.  He had tantrums 3 times a day every day.  He is better after a year of occupational therapy, in home mental health help and outpatient counseling.

  Some of the things you have described sound like that, although extreme.  I'm no expert though by any means.   I have sensory issues too, (so does my daughter), both of us mainly with clothing.  I have learned to deal with it as I got older.  I don't wear socks-no big deal.  But when I worked I did or I wore nylons.  I don't like jeans but wear them b/c you just can't wear knit pants all the time.  I change my clothes into my lounge wear as soon as I get home.  I can't stand strong "smelly" perfume but sometimes you just can't get away from that person.  Once while eating out, a family sat next to us with that perfume and I couldn't finish eating, but I couldn't ask to be moved, she would have heard me say way.  So I made my family eat faster so we could leave quickly!

The overexgerrating doesn't sound like SPD though, don't know what that could be.  That is annoying.  I don't know what advice to give for an adult with these issues.  Maybe he can start with talking to his primary care doctor?