Thanks for the extra info. It sounds like there's something more going on than typical mating or bonding behavior (regurgitation) and it also seems that you're pretty on top of it. Very good instincts (trust them!).
Holding the wings out and down, the flutter you're seeing, may be an indication of overheating. Are his feet warmer than usual ? If so, gently spritz them with cool water or slowly pour a little cup of water over them (try not to frighten him or stress him).
The motions you're describing with the head motion and how he's chewing, would be in keeping with a crop and/or mouth infection. This will be a messy, sticky substance, often clear or cloudy, sometimes with food in it. It'll end up on top of his head, around the cage - very obviously not the neat package of regurgitation you've seen before.
If possible, collect a sample of this substance to bring to the vet with you.
When there's a blood showing in the vomitus it may indicate esophageal or proventricular ulcers (http://www.multiscope.com/hotspot/pdd.htm) .
The vet will take a look into your bird's mouth for other symptoms and I'd ask for a swab culture if the vet isn't going to do one anyway. A good exam will also check for any growths or tumors. Unfortunately these are pretty common in parakeets.
Vomiting is a more serious symptom and seeing a vet as soon as possible is important. There are far too many possible diseases to outline here, but as in any case of illness, getting it evaluated, diagnosed and treated right away is often the best outcome at the lowest cost.
The top causes of vomiting in domestic birds are (gram-negative) bacteria, something that may increase to a troublesome point after the bird is stressed somehow. Stress can involve changes in their environment, being frightened, having their sleep hours reduced or other changes in schedules or even a difference in food.
The other possible causes are contamination of food or water by fecal matter. Be sure there are no perches above food/water bowls which could allow this to happen without you noticing until after the bird has ingested it.
Candida (also increased after a stressor) infection or Trichomonas are also causes that should be explored by your vet. When these are all ruled out, the search for a cause can get pretty complicated.
Have an eyedropper ready to administer a few drops of plain water, or better yet, children's Pedialyte every 20-30 minutes. Put the dropper gently inside the beak and let the drops fall into the bottom beak under the tongue rather than trying to get into the back of the throat. We don't want to chance the bird inhaling the fluid and developing pneumonia.
Another feeding option is to offer ½ spoon of all natural, organic baby food (squash, yams, sweet potatoes, mixed vegetables) which many birds take readily; also try some pabulum or baby rice cereal and a few licks of natural (no artificial anything) yogurt.
These are just temporary supportive measures to keep your bird alive while you get professional, hands on care. These measures will not cure your bird.
Don't mistake what looks like recovery to be a real recovery. It is very common for a bird to regain enough strength to start hiding their illness again, but what's happening is that it's progressing and by the time you see symptoms again, it will be much worse or too late.