Around the lake you are not going to find U.S.-level medical facilities (you will find them in Guatemala City) but what you will find is decent care at low prices. For example, if you need to go to a hospital emergency room, the ambulance is free and the care is free. Paperwork? Virtually nothing beyond asking you your name.
Public Health Clinics
The first level of free care are the public health clinics. Government funded (or, more accurately, underfunded) they offer basic care. They even may surprise you with some of the things they now offer. Psychological care. Accupuncture.
The care is available to anyone who walks in. Here is an example which surprised even me.
A woman in her early 20s was on vacation here with family. She wanted an under-skin contraceptive chip implanted but it would have cost her $500 in the U.S. She went to the Centro de Salud to inquire. She left with the chip implanted. Total cost: $0 and she was just here as a tourist.
In San Antonio, the Public Health Clinic is located across the street (more or less) from the soccer field. The ambulance is usually parketed in front of it.
Other Local Care
There are lots of local doctors and, in Panajachel, a privately-run free health clinic. The private clinic in Panajachel gets good reviews and the doctor (Dr. Luis is how he is known) speaks English. That may be a plus for you. It is located a bit north of Calle Santander on 15 de Febrero. Information on the clinic is available at Atitlan Wellness Clinic. While the primary focus of the clinic is to help those who cannot afford other options, I think a few of us who can afford care elsewhere, visiting and donating generously is going to help them stay open.
For private doctors, prices are likely to fall in the Q100-Q300 range for an office visit. Drugs will be extra.
A friend needed a hernia operation. He found a doctor he liked and the operation could have been done in the public hospital for free. (Doctors with a real practice are required to volunteer a certain amount of time in the public hospitals.) But, the doctor suggested doing it in a private one. Total cost for doctors, nurses, operating room and one night stay in a private room was $800.
Some good, some bad but they certainly exist. I use and many of my friends have used “Dra. Lily” in Panajachel on Calle Santander, above Banco Industrial. The second time I went for an appointment I heard her talking to her patient in English. So, that could be a plus. Fillings seem to be Q300 (as I remember). We paid for a 6-tooth bridge and some fillings for Rocio’s mother. It was about Q2500.
Also, across the street from her office in Plaza Atitlan is another dentist/oral surgeon. I have a friend who has gone to her to have his wisdom teeth removed and is very satisfied.
The closest government hospital (thus, free) is in Sololá. There is nothing fancy there but they seem to get the job done. My daughter had her appendix removed there with no problems (or cost). My niece was taken there for X-rays after she fell (OK, she was in a fist fight with another girl) and hurt her back.) Again, no cost including a free ambulance trip.
If you are looking for serious medical options, there seem to be a lot in both Guatemala City and in Quetzaltenango (Xela). Both cities have medical schools. I have been told that the teaching hospital in Xela is quite good.
Like hospitals, there are options for ambulances as well. In most towns (Panajachel and San Antonio are no exception) there is a free volunteer ambulance service. In Panajachel it is part of the services of the Volunteer Fire Department (Bomberos Voluntarios). Not sure in San Antonio but the ambulance is usually parted near the soccer field.