and I too have "forgotten" to breathe during my waking hours. Not sure why it happens. I also suffer from extreme bloating from IBS, and the MS hug, where the intercostal muscles between the ribs spasm and tighten my chest. So those might be factors. I can totally relate to the situations you describe.
In addition, a nurse once listened to my lungs and said she heard rales ( a.k.a. crackles, rhonchi) and said it appear when people shallow-breathe most of the time. She advised me to practice taking deeper breaths. That will keep fluid from settling in my lungs.
So I try to catch myself not-breathing, and then take some deep breaths soon after.
Moreover, I was recently diagnosed with severe sleep apnea! I use a CPAP machine and medium face mask. It has improved my breathing and reduced the number of times I stop breathing every hour from 30 to 5! But I still wake up several times during the night and often do not get enough sleep. This can contribute to daytime drowsiness.
Medications are another thing that might contribute to or cause that narcoleptic sudden loss of consciousness while alert and fully engaged. I take a very high dose of baclofen, and it could have that effect, especially if I didn't get enough sleep on top of that. If you take an anti-anxiety med during the day, who knows, that could contribute to drowsiness and slowed or stopped breathing.
We need to tell our medical team about these things. If they don't know about it, they can't help us. --Kim, moderator