'Simulated slumber' is a phrase that can be used in place of 'pretended to sleep.' Another option is 'feigned rest,' which can imply a deliberate act of pretending. 'Faked dozing' is another alternative with a slightly negative connotation, suggesting that the person deliberately misled someone else. 'Pretended slumber' is a more direct synonym and is commonly seen in literature and film. 'Acted asleep' is another option that doesn't necessarily imply deceit but still conveys the idea of pretending. Overall, there are many synonyms for 'pretended to sleep' depending on the tone and context desired.