There was a completely reasonable answer as to why Heatwave decided to keep quiet after that day.
After his seizing accident, he started to have issues with his memory, which he later found to be because his spark broke after hearing that his creators were not coming back for him. There would be multiple times where he forgot a ton of things and sometimes when they came back to him, it felt like a strange dream.
it was very frequent at first, which made it very difficult for Heatwave and somehow resulted in more seizing moments. it eventually did end up stopping at some point but Heatwave never found a point to say anything because none of the medics would've cared anyway.
Heatwave knew Starlight cared, but he could always sense this thought that the medics might make her leave and then his life would end up turning into torture. As a result of his own worries, he keeps himself quiet so he doesn't lose more than he can handle.

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Transformers Rescue Bots - The Past
FanfictionThe timeline to how the 4 main Rescue bots go from their creation to Griffin Rock, many stories in order full of the depths of their lives before getting on the Sigma 17 that fateful day and eventually going to earth. Dive in as we follow the years...