There's a slight increase in the blood pressure in your upper body, and a small possibility of thrombosis, blood clots forming in your veins. But after 50+ years of space flight no one has had complications.

Veins are small so capillary action keeps things in order.

With no gravity though you'll have higher blood pressure to your head (and less to the legs)- it kinda makes astronauts faces a bit puffy. iirc this can slightly negatively affect vision long term.

Most of your body processes are in a small enough space that capillary action overtakes gravity.

If you put it on a sandwich, yes.