Drowsy after stretches

Iam 35f 1 year Postpartum I've noticed that immediately after stretching light stretching I'll become drowsy . My eyes will not shut but become heavy and i nod forward to relax my neck. Any idea of what could be going on . I do have my days and nights mixed up so maybe has to do with not enough rest i am 120lb 5'5. Im not tired just feel heavy and drowsy in the neck and head area and eyes. Its weird cause i have to sit down and then i contemplating whether to get back in bed .