Is Throwing Up Brownish Green With Heartburn, Serious Medical Condition After Laparoscopic Hernia?

Hello. My father (70 y.o) had an extensive laparascopic hernia surgery on 1/9/14. He was kept in the hospital overnight and discharged in the afternoon. He is passing liquids fine, but has no appetite and eats very little. He burps a lot, but does not pass gas. Also he did not have bowel movement yet even though he took Miralax for the 3-d time today (1/13/14). Yesterday he threw up brown - green stuff twice - in the morning and in the evening. He also complains of heartburn. He had his gallbladder removed many years ago. Is throwing up brown - green serious medical condition? Should he go back to the hospital? Is it OK to take Nexium to help with heartburn?