Thanks for your question on Healthcare Magic.
I can understand your concern.
It is quite possible that you might be having hair line feature that is causing this worsening pain and symptoms after 12 hours of fall.
So in my opinion, you should first get done
x ray of affected thigh to rule out hairline
fracture.
If x ray is normal then no need to worry for this.
Sometimes inflammation in the injured muscle can cause worsening of symptoms after 6-10 hours.
So avoid movements especially weight bearing.
Apply warm water pad on affected areas.
Take painkiller and anti inflammatory drugs.
Take proper
bed rest with minimal mobilization.
Don't worry, you will be alright with all these in 1-2 weeks. But better to first get done x ray to rule out hairline fracture.
Hope I have solved your query .I will be happy to help you further. Wish you good health. Thanks.