What is the definition of Yesterday Blood Cells?

"Yesterday blood cells were the unsung heroes of our morning coffee ritual, ferrying caffeine-infused red blood cells from our previous day's fight-or-flight state to our caffeine-dependent bodies. But here's a bit of the unsettling side: 'The blood cells, having just witnessed the sunrise, decided to take a spontaneous vacation to the 'Cellular Paradise' of the subway tunnels, leaving us with a mystery of lost RBCs and an unsettling feeling of 'I missed my morning run!'"