Been working in the garden, suddenly felt dizzy, got an upset stomach leg started twitching, started to sweat lot. Are these early signs heat stroke?

It’s a sign of heat exhaustion, which is not heat stroke, but a step on the way to heat stroke. People with heat stroke actually stop sweating. Sudden increased sweating fits heat exhaustion better, especially with the other symptoms. Hopefully you moved to a cool place & started sipping water. Also super good is if you can wear your top, and out cool clothes on your sternum, neck, wrists, and inner thighs. Heat exhaustion needs to be treated and quickly to avoid moving to heat stroke where bad things happen.