Our sleep patterns are such fickle things. The slightest disturbance can shift it by several hours. Wake up unusually early one morning and you fall asleep earlier the next night. Now your sleep schedule has shifted. Getting it back to what it was can be a challenge.
I just got back home with a 14 hour time difference and my sleep is all over the place. It takes my body about a week or two to realise something's changed. I find myself awake in the early morning hours and struggling to stay awake in the afternoon. Time is relative, so our bodies function according to the time it observes. When you make significant timezone switches your body doesn't care that the sun rises several hours earlier than before. All it knows is the time it's grown accustomed to.
In both cases, it takes a significant effort to get your desired sleep schedule back. For something so important to our functioning, we have very little direct control of it. We can't clock our eight hours in whenever we want to. We can't stockpile those hours for a rainy day. When your sleep pattern gets disrupted you have to almost trick your body into recognising the change and reverting to its old ways. With enough effort, you're eventually back to normal. But with an appreciation for how volatile and yet out of your control a good night's sleep can be.