Did you change the water you soaked them in?
Lentils & other pulses contain sugars that humans cannot digest,
but,
the gut flora in your intestines can.
If you don't change the water the lentils were soaked in,
and for best results, the water that is used to bring the lentils to a simmer/boil,
you eat these non-digestible sugars and suffer the consequences the following day.
Did you change the water you soaked them in?
Lentils & other pulses contain sugars that humans cannot digest,
but,
the gut flora in your intestines can.
If you don't change the water the lentils were soaked in,
and for best results, the water that is used to bring the lentils to a simmer/boil,
you eat these non-digestible sugars and suffer the consequences the following day.