Learn Hardcore Japanese: nemukute sofa de sonomama netyatte, syukudai wo dasuno wo wasureta. - I was sleepy and ended up falling asleep on the sofa, and I forgot to turn in my homework.

Breakdown of nemukute sofa de sonomama nechatte, shukudai o dasuno o wasureta.

Why is 眠い changed to 眠くて?

眠くて is the -te form of the i-adjective 眠い.

For i-adjectives, you usually make the -te form by changing -い to -くて:

Here, 眠くて links to the next action and gives a reason/background sense:

So it is not just “sleepy and…” mechanically; it often feels like “because I was sleepy…” or “being sleepy, …”.

What does ソファで mean here, and why is で used instead of に?