Relationships

I usually can't wake up my boyfriend from his sleep but he easily wakes up when im crying?

I've been with my boyfriend for almost a year and we've moved in together. he's usually a very deep sleeper. he sleep talks (very clearly, sometimes i think he's actually talking to me) and moves around as if he was awake. usually he falls asleep within 5 minutes of laying down no matter what time of the day, and i take between 15 minutes to a couple hours and sometimes ill try to wake him up by gently pushing my body against him or pushing him lightly, enough to make him move. sometimes ill play around with his arms or jus caress along his body. i'd get out of bed, get water or play with the cat then get back in bed loudly and he does not wake up. sometimes his alarm which is right beside his head doesn't wake him up. however, last night i was having trouble sleeping, was in bed for about 6 hours and started getting a headache which led to me crying. however after about 5 mins of me silently crying only with audible breathes, he woke up. he said "why are u crying. dont cry baby". and i told him i couldnt sleep and he said its nothing to cry about and within 2 minutes he fell asleep again. this morning i asked him how he woke up because he never wakes up during the night, his reply was "its human nature to wake up to a baby crying".
so my question is, is this really the case? that humans will wake up from hearing distress, or was it just by chance that he woke up?

I usually can't wake up my boyfriend from his sleep but he easily wakes up when im crying?
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