The power of ...bread

I bought buns from that chinese bread shop at the bottom of Sussex St after ELEC3006 lab tonight. Caught a train home and just like last Thursday, dozed off around Strathfield, missed my stop (West Ryde) and ended up getting off at Eastwood. My sister used the car so I couldn't ask for a lift home and had to wait for a train back to West Ryde. Added an extra 45mins to the trip. Seriously, what do they put in those bread that makes me so sleepy every time I eat them?