Reference for Shabbat 258:3

אמר שמואל פורסא דדמא כל תלתין יומין ובין הפרקים ימעט ובין הפרקים יחזור וימעט

Rab and Samuel both say: One who is bled should tarry awhile and then rise, for a Master said: In five cases one is nearer to death than to life. And these are they: When one eats and [immediately] rises, drinks and rises, sleeps and rises, lets blood and rises, and cohabits and rises.

Jastrow