Ask HN: Internet magically gets faster when opening speedtest?

I want to start by saying this is anecdotal, and I feel paranoid for even thinking it. But often my internet will feel very slow, so I'll open speedtest to check if something's wrong. When I do, all of my stalled tabs suddenly spring into action and finish loading.

The tinfoil hat wearer inside of me speculates that my internet provider is overloaded and throttling my bandwidth, but immediately prioritizes me when it senses that I'm trying to check if I'm getting what I pay for.

Has anyone else noticed this pattern? Is there a way I can test this more scientifically?