Toxin release, above average?

Dear Yoga Community,

My name is Frédéric, I practicing yoga Since around 5 years. Until now I still have my problems with Uttanasana or front bends in general. My backside is very short, that’s why the stretching progress is very low.
That’s why I decided to do a intense stretching workout, 15min, 2 times a day with different front bends asanas. Plus normal yoga practice.

I do this since 10 days now, the process is amazing but after the first 3 days my immune system felled down and I had 2 days body aches and headaches, feeling week. On the 5th day I was fit again and started slowly with my workout. Again 3 days later I’m ill, same symptoms plus a bit fever.

I living since many years in Thailand and during this time I never was sick.

Is it possible that this intense stretchings are releasing an above average amount of toxins and harming my immune system? Deposited toxins that may stuck in the soft tissue since years.?

(I still stretched carefully, only being longer in the positions)

Looking forward to your feedbacks. Thank you in advance!