I think it depends on the pregnancy.
I was pregnant with DS2 when DS1 was a toddler. I cruised through wasn't too tired, no M/S.

Where as if I'd had a toddler to look after during this pg I couldn't have coped I was just too sick I litterally couldn't get out of bed for the first 9 weeks except to use the toilet.

So luck of the pregnancy I think, goood luck