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Should I be shitting myself?
No. It's been there since Victorian times and as the roof is presumably made of wooden joists/rafters some movement is to be expected. My parents' house (built 1968) has a wooden frame with tiles over it for the first floor instead of brick and does the same thing.
That said, if you're really worried about it get the joists/rafters looked at to check they're still structurally sound.
My house is shaking in the wind. 4 storey late Victorian terrace (of 4 houses), we’re one from the end eastern end and fairly exposed to wind off the estuary as we’re 2 stories taller than the surrounding houses. We sleep in the top floor in the eaves and the house is shaking in high gusts. Fairly subtle but definitely happening. It woke me up. Should I be shitting myself?