Known causes for head tilt in domestic animals include:

Encephalitozoon cuniculi (or E. cuniculi) infection in rabbits
parasitic infestation by the nematode (roundworm) Baylisascaris procyonis in rabbits
Inner ear infection
Hypothyroidism in dogs
Disease of the VIIIth cranial nerve the N. Vestibulocochlearis through trauma, infection, inflammation or neoplasia
Disease of the brain stem through either stroke, trauma or neoplasia
Damage to the vestibular organ due to toxicity, inflammation or impaired blood supply
Geriatric vestibular syndrome in dogs

Notes
References
External links
Head Tilt: Causes and Treatment
This is done on either side. If this is not sufficiently effective, then cold normal saline may be injected and removed. Medications
If aspiration is not sufficient, a small dose of phenylephrine may be injected into the corpus cavernosum. Side effects of phenylephrine may include: high blood pressure, slow heart rate, and arrhythmia. If this medication is used, it is recommended that people be monitored for at least an hour after. For those with recurrent ischemic priapism, diethylstilbestrol (DES) or terbutaline may be tried. Surgery
Distal shunts, such as the Winters, involve puncturing the glans (the distal part of the penis) into one of the cavernosa, where the old, stagnant blood is held. This causes the blood to leave the penis and return to the circulation. This procedure can be performed by a urologist at the bedside. Winters shunts are often the first invasive technique used, especially in hematologically induced priapism, as it is relatively simple and repeatable.Proximal shunts, such as the Quackels, are more involved and entail operative dissection in the perineum where the corpora meet the spongiosum while making an incision in both and suturing both openings together. Shunts created between the corpora cavernosa and great saphenous vein called a Grayhack shunt can be done though this technique is rarely used.As the complication rates with prolonged priapism are high, early penile prosthesis implantation may be considered. As well as allowing early resumption of sexual activity, early implantation can avoid the formation of dense fibrosis and, hence, a shortened penis.