Hello from JustAnswer.
The most common cause of acute diarrhea is an infection of the GI tract, which can be either viral or bacterial. For either infection, it will typically resolve spontaneously and if it is not causing any complications, supportive care is all that is indicated. Even bacterial infections will usually improve without antibiotics, although antibiotics may still be necessary for more severe infections.
From your description, though, the major concern is that you may be getting dehydrated. Dehydration can occur with any infection causing severe diarrhea, but in hot weather and loss of fluid from sweat, it is easier to become dehydrated.
If you can drink large amounts of clear fluids, particularly clear fluids that contain electrolytes, such as sports drinks, and your raging thirst eases, then that would be a good sign that your hydration status is improving. It would be OK to continue the Imodium.
However, if the raging thirst does not improve or you develop more worrisome signs of worsening dehydration, such as lightheadedness or dizziness, then it would be better for you to be seen, such as at an Urgent Care Center or Walk-In Clinic.
If I can provide any additional information, please let me know.
Please let me know if I can provide any further assistance.