A thermal comfort field survey in sleep environments was conducted in Qatar during winter and spring seasons. A total of 833 sets of objective and subjective thermal and sleep quality responses before going to bed and after getting up were collected. The subjects felt cooler sensations most of the time, preferred warmer sensations and the sleep environments are considered comfortable overall. Griffiths comfort temperature (Tc) was 24.3 ˚C and 20.2 ˚C in free-running (FR) and air-conditioned (AC) modes respectively. Subjects used air-conditioner (AC)s adaptively in heating mode in winter. In 82.7% of cases in (AC) mode, the comfort temperature was below the lower limit of the international standard. Subjects enjoyed quality sleep in Qatar. Overall, self-declared sleep quality improved with thermal acceptability. Depth of sleep was higher in AC mode (mean = 3.86). On the other hand, the mean global Pittsburgh Sleep Quality Index (PSQI) score was high in general (mean = 10.7), indicating good quality sleep, and significantly so in free-running mode (mean = 11) than in AC mode (mean = 10.4). It increased, as subjects liked their AC systems. This study suggests that overcooling in spring can be avoided by increasing air movement without compromising sleep quality.