I secretly act like I'm asleep so my roommates let the dog out and not me
Why do you not want to let the dog out?
Uh, no, I just got lazy
You are responsible for your dog, not your roommates so you should be letting your dog out.  If you keep pretending to sleep, your roommates might start to resent you and could start causing drama.  No one wants to live with someone who's lazy and can't take care of their duties.
Too bad for them if they made a big deal out of a small thing
I do not think that you should take advantage of your roomate's kindness. I think that you should be the one taking care of your pet.