A lot of it boils down to blood pressure. High blood pressure is a serious contributing factor to cardiovascular incidents (as well as a slew of other negative health risks), and getting a good night's sleep will help keep blood pressure down. This is also why the amount of heart attacks are up around 24% after daylight savings[1]; an hour less sleep means higher blood pressure means higher risk of heart attack (relative to any other 'normal' day).
I can definitely see how the same logic could apply to Mondays. Less sleep, more stress = higher blood pressure = higher risk of heart attacks.
[0] https://www.goodreads.com/book/show/34466963-why-we-sleep
I think many people do the same sort of thing, and then monday -- they have to cut their sleep short to get up early and sync with the rest of the world.
I can see how this would be the stressor you allude to.
The only problem is it's often incompatible with a social life when you're in your 20s, but thankfully I'm not in my 20s anymore.