Background: Sleep disturbances in bipolar disorder exert negative impact. Here we report a case of bipolar disorder, who had manic relapse due to decreased sleep because of waking up early during religious festivities. Case description: Mrs S is a 50-year-old married Muslim lady was diagnosed to have bipolar affective disorder (BPAD) for the past 25 years. Till now, she had about 8 to 10 manic episodes. From December 2017, she has remained euthymic, being compliant on tab. lithium 1200 μg/day (serum lithium level: 0.79 mmol/L). During her scheduled follow-up (May 25, 2019), she reported decreased need for sleep, grandiose ideas, increased psychomotor activity and energy from the start of Ramadan, about 20 days ago. During these 20 days, she woke up about 2 hours earlier to prepare food for family. She was compliant on lithium. Her Young Mania Rating Scale (YMRS) score on the first day was 19, showing manic levels and the Pittsburgh Sleep Quality Index (PSQI) was 12, showing poor sleep. Tab. olanzapine 30 μg/day was added to lithium 1200 μg/day. She showed gradual improvement in quality and quantity of sleep and was discharged after 2 weeks (June 09, 2019), with tab. lithium 1200 μg/day and tab. olanzapine 10 μg/day. The patient and her family were psychoeducated regarding the importance of sleep and compliance. During the next follow-up after 5 days, she showed improvements. Conclusion: Sleep architecture changes in rapid eye movement (REM) sleep like shortened latency and increased density may contribute toward hypomanic/manic symptoms. In bipolar disorder, sleep disturbances even on one previous night may subsequently change the mood toward mania, in spite of having adequate serum lithium levels. Clinical significance: Psychiatrists need to be vigilant regarding this and provide psychoeducation on sleep hygiene especially with sleep deprivation.