Why Do I Feel Nauseous After I Nap....I Have A

Why do I feel nauseous after I nap....I have a 2.5 year old and every day when she naps I do lay across the bed and fall asleep....it doesn't matter if she wakes me on the monitor or if I get up on my own. I always feel nauseous and literally sick to my stomach like I could vomit? Is there any answer to this? I do feel nauseous at other times (randomly) like in the evening before bed or after I eat sometimes. The only medications I take is Zoloft. I have been taking for over 2 years though!