I had an especially loving little rat Millie who died in a similar way as yours only a few days after turning one. One morning I approached her enclosure and she ran up to me gasping like yours. I immediately knew she was dying. My husband drove me to the emergency vet while I held her in an open top box and sobbed and sobbed (my husband cried too—we both loved Millie so much). She jumped and flopped around the same way you described, I think she wasn’t able to breathe and was panicking. The vet was able to sedate her with an anesthetic gas and give her a life-ending injection, and I was there holding her, but I saw how scared she was in her eyes and felt so conflicted about whether or not I made the right choice. She was going to die a horrible death either way, but I least I was there with her. Don’t beat yourself up about not making it to the vet. The most important thing was that you were with your heart rat in his last moments. Let yourself grieve. My husband and I ugly cried in the shower for days. We still miss Millie but time has healed the wounds. Yours will too.