There's a cloud cover and the humidity feels higher. The air is
  thicker and i feel "bigger". I think perhaps there is a
  low-pressure system that is causing my body to expand, retain a
  little more water, making me sluggish and everything heavy.

  It's not a dramatic difference, but it's noticeable. My arms
  don't want to leave the computer table even to have a sip of
  coffee.