I'm sorry that your question wasn't answered in a timely manner. We don't have many avian vets on this site.
A bird that bobs its head up and down in a sort of pumping motion, beak open and then a purposeful delivery of partially digested food is regurgitating. This is something they would do to feed offspring or a mate. It’s done by some birds to objects (toys, mirrors, people) they are particularly fond of - especially if they’re in a breeding season, when a bird wants to please their owner and/or is of a nervous temperament.
Regurgitation that is unusual enough for you to make note of it like you have, might be a symptom of crop infection/impaction and it’s a threat because it can lead to malnourishment. If your bird is giving up too much of the food they should be digesting for their own nutrition, malnutrition may arise.
Vomiting is more of a head “flicking” event. The bird will often seem uneasy, pacing or uncomfortable and although the head bobbing might be similar to the regurgitation action, it’s usually more of a shaking and the end result is a very splattered, sticky substance that may or may not include food. When there’s a blood showing in the vomitus it may indicate esophageal or proventricular ulcers. You appear to be describing Guava vomiting.
An avian vet (please see here: www.aav.org) will take a look into your bird’s mouth for other symptoms and is likely to examine a swab of the oral cavity for abnormal numbers of either bacteria, yeast, or parasites. A good exam will also check for any growths or tumors.
Vomiting is a more serious symptom and seeing a vet as soon as possible is important.
There are far too many possible diseases to list 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.
A common cause of vomiting in domestic birds is gram-negative bacterial infections which may have exacerbated after a bird is stressed. 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. Another possible cause is contamination of food or water by fecal matter.
If your bird will drink and eat on its own please consider eyedroppering 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. Please heat up his environment to 85F so he need not expend excess energy keeping his body temperature up.
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. Nutritional imbalances are a common cause of illness in our pet birds. What has Guava's diet consisted of, please? Seeds should compose less than 20% of his diet. Ideally, a balanced pelleted diet such as can be found here: www.harrisonsbirdfoods.com or here: www.lafeber.com/pet-birds should be fed as well as hard boiled egg yolk, pancakes and cornbread, the tops of fresh greens, dairy products such as yogurt and cheese, fresh fruits such as apples, pears, melon, kiwi, and berries, vegetables such as broccoli, carrots, beets, asparagus, cabbage, sweet potato, and squash, and even tiny pieces of meat.
Please respond with further questions or concerns if you wish.