Viral Gastroenteritis: This is the most likely diagnosis given the symptoms of nausea and vomiting after a vacation, which could have exposed the patient to various pathogens. The lowered alkaline phosphatase (alk phos) and neutrophils could be consistent with a viral infection affecting the gastrointestinal system and potentially impacting liver function and white blood cell count.

Food Poisoning: Similar to viral gastroenteritis, food poisoning from consuming contaminated food or water during the vacation could lead to nausea, vomiting, and alterations in lab results due to the body's response to the toxin or pathogen.
Traveler's Diarrhea: Although primarily causing diarrhea, traveler's diarrhea can also lead to nausea and vomiting. The condition is common in travelers to certain regions and could explain the patient's symptoms and lab abnormalities.

Hepatitis: Although less likely, hepatitis (especially viral hepatitis) is a critical diagnosis not to miss. It can cause nausea, vomiting, and alterations in liver enzymes, including a decrease in alkaline phosphatase in some cases. The consequences of missing this diagnosis could be severe.
Typhoid Fever: This condition, caused by Salmonella Typhi, can present with nausea, vomiting, and fever. It's particularly relevant for travelers to endemic areas. Missing this diagnosis could lead to severe complications, including death if not treated promptly.
Appendicitis: Although the symptoms might not fully align, appendicitis can sometimes present atypically, especially in early stages. The lowered neutrophil count might not be typical for appendicitis, but it's a condition that requires urgent surgical intervention to prevent serious complications.

Cyclic Vomiting Syndrome: A rare condition characterized by recurrent episodes of severe vomiting. It could be considered if the patient has a history of similar episodes, although the lab abnormalities might not fully align.
Whipple's Disease: A rare, systemic bacterial infection that can cause gastrointestinal symptoms among others. It's very uncommon and would typically require more specific symptoms and diagnostic findings to consider.
Giardiasis: An intestinal infection caused by the parasite Giardia lamblia. It can lead to gastrointestinal symptoms but is less likely to cause significant alterations in blood tests like the ones described.