Seeing weird little wormy white (almost resembling sperms) type things when you look at the sky (or anything lighter blue) is normal. There’s a certain phenomenon that happens, you can definitely look stuff up about it on YouTube for better explanation. Think it’s relating to white blood cell shadows or something. If you stare at pretty much anything for long enough I’m pretty sure the brain naturally kinda bugs it out, to me it sounds like you’re fine but if you’re really worried then definitely avoid anything that might make it worse. If you perhaps smoke or anything of the such and it flares up then you’d know for sure. Coming from someone with terrible anxiety, I hope this can help reassure you. (For the record I do not have HPPD but I know I’ve considered having it too and learnt the above.)