What Could Cause Sudden Dizziness, Blurred Vision, Vomiting, And Loss Of Coordination In My Colleague?

Hi,yesterday after work,my colleague just started feeling dizzy,blurred vision,vomiting and suddenly couldn't coordinate his walking step and needed support. We hadn't eaten the whole day but we had water . He had taken at least 1.5 liters of water. we are managing a construction site and the area can get pretty hot.
Please assist as we still don't know what could be going on. We visited a clinic immediately and they took his vitals and blood sugar ,all was normal