I can't stop crying! One of my bunnies went exactly the same way. She was given to us by a fellow that adored her but could not spend enough time with her and he had rescued her from people that had her locked in a small cage in a dark garage. We only had her a short time but she was so affectionate and loving. She always wanted to be in my arms. She would follow me around the house and beg to picked up. Her favourite was to get all snug in bed with me, laying on my chest with only her head sticking out from under the covers. I would pat her head until I fell asleep, then she would wake me up because I stopped patting her.
When I took her to the vet, I was confident it was nothing serious. By the time we walked out the door, she was gone. Cancer had spread to her lungs and her laboured breathing was due to this. The vet said it would be cruel to let her go, even for a day, as she was so far gone. I held her in my arms as she was given the injection. I was in shock for weeks after.
I am so, so sorry for you and your little Sekura. My heart goes out to you!
Kathy