A seed should be expelled in the stool. You shouldn't have symptoms like that from swallowing a seed. What else did you eat that day? Maybe the lemon was tainted. Agree that you should see a Dr. to r/o food poisoning/other causes if symptoms persist; and stay well hydrated, esp. if you're having vomiting/diarrhea.
Good luck.
A seed should just follow normal digestive processes.
Did it go down the wrong way? Your symptoms may be unrelated to the seed.
I would try and stay well hydrated and talk to your doctor if your symptoms persist or you have concerns.
Im not sure a lemon seed could do that unless it was tainted with something. You should probably see a doctor for blood work and to make sure you somehow do now have food poisoning.