Here is a list of some of the most frequent illnesses and disorders that may need seeking medical attention. Remember to express your problem clearly: if the dispatcher understands what's going on, the ambulance will be able to assist you as soon as it arrives. Furthermore, you will receive the most accurate and well-informed counsel possible, based on your specific circumstances.

Japanese language book like this one below can also be helpful.

Illness and Conditions in Japanese

If it is emergency and you would like to ask someone to call an ambulance, you can say "Kyukyu-sha o yonde kudasai (please call an ambulance)".

Please also refer to Emergency Telephone Numbers in Japan.

Having Pain / Feeling Sick

I am feeling sick.
Guaiga warui desu.

Chest pain
Mune ga itai desu.

Headache
Atama ga itai desu.

Stomachache
Iga itai desu.

Lower abdominal pain
Onaka ga itai desu.

Throat pain
Nodo ga itai desu.

Others

Allergic reaction
Arerugi desu.

Feeling dizzy
Memai ga shimasu.

Feeling nauseous
Hakike ga shimasu.

Having a cough
Seki ga demasu.

Having a fever
Netsu ga arimasu.

Having a stuffy nose
Hana ga tsumatte imasu.

Having a runny nose
Hana ga demasu.

Having diarrhea
Geri o shite imasu.

I'm pregnant.
Ninshin shite imasu.

Symptoms in Japanese

Bleeding
Shukketsu

Chill
Okan

Constipation
Benpi

Convulsion
Keiren

Cough
Seki

Diabetes
Tou-nyo-byo

Diarrhea
Geri

Dull
Darui

Fever
Netsu 

Hypertension
Kou ketsuatsu

Hypotension
Tei ketsuatsu 

Injured
Kega

Irregular periods
Fusei shukketsu

Itching
Kayui

Nausea
Hakike

Nose bleeding
Hanazi

Numbness
Shibire

Pain
Itai

Palpitation
Douki

Rashes
Shisshin

Pregnancy
Ninshin

Runny nose
Hanamizu

Seizure
Hossa

Shivering
Furue

Spasm
Keiren

Swelling
Hare

Please also refer to "I am sick, I want to see a doctor" from AMDA.

Other useful information

・Health Care in Japan

・English-Friendly Hospital Services

・English-Speaking Hospitals in Japan

・Medical Emergencies: How to Communicate in Japanese