I have never slept next to Kate. The only thing we do in bed is have sex. We have separate beds and homes. Should you do the same? Not necessarily. The science is split. Here's the data: 1) Your partner does wake you up when you sleep together. 7 nights of actigraphy sleep measurement in 55 couples (aged 18 to 72, no sleep disorders) showed about 6 partner triggered awakenings per night, on average. Roughly 1 in 5 of wake ups was set off by the partner stirring first, and participants slept through only about half of their partner’s awake time. The catch: the study never compared sharing a bed to sleeping alone. 2) Yet couples who sleep together report sleeping better. A survey of about 1,000 adults found that sharing a bed with a partner tracked with less insomnia, less fatigue, more sleep, and better mental health than sleeping alone. The catch: self-reported, cross-sectional, no follow-up. Healthier, happier people may simply be the ones more likely to share beds, so this is associative at best. 3) Women's sleep might take the hit from sharing a bed. A study of 10 couples had each person sleep at least 10 nights alone and 10 nights together. Women slept measurably worse with a partner in the bed, on both actigraphy and their own ratings. Men reported sleeping better, subjectively. 4) Polysomnography, the gold standard for measuring sleep and sleep stages, points to REM gains with co-sleeping. A study of 12 couples found co-sleeping came with about 10% more REM sleep, less fragmented REM, longer undisturbed REM runs, and tighter sleep-stage syncing between partners, alongside more limb movement. 5) Synced sleep tracks with lower blood pressure and inflammation. In 46 couples that slept together, the more in sync their sleepwake timing, the lower their sleeping blood pressure (strongest in women) and the lower their inflammation (both sexes). The link held even after adjusting for how often they actually shared a bed, so the driver looks like the synchrony, not sharing the bed. Only two of these studies compared the same person in both beds, and both are tiny: 10 and 12 couples. One found the result flips by sex. The rest is correlation. The answer is individual. For some couples the shared bed improves sleep. For others, separate beds are the right move.