There are a number of conditions that are related to 'dry retching' (or 'heaving'), where your body creates vomiting-like sensations but you're not actually sick, i.e., nothing comes up. When people dry retch after drinking too much, it usually happens once the person has finished vomiting and, as you say, there's simply not enough material left to throw up.
People vomit after drinking because our bodies try to protect us from alcohol poisoning by preventing unabsorbed alcohol from reaching the brain. Specialised poison control cells send messages to the stomach to empty its contents, i.e., to vomit. Even though the alcohol may have all been expelled, those messages that kick-started the vomiting may still be active. The brain has no way of directly knowing how much alcohol still remains, so the message to keep emptying the contents of the stomach may continue, resulting in dry retching.
Dry retching is often described as much more painful and traumatic than the rest of the vomiting process and can also be quite frightening for the person looking after the drunk person. If dry retching persists, it can, in extreme cases, result in damage to the oesophagus, causing bleeding and tearing. If this occurs it is vital that the person is treated by medical professionals and you need to call 000 immediately.
First published: July 2021