How can i go into ketosis by accident?

No insulin: The only way to go into ketosis is not eat or not take your Insulin if you require injections. Without Insulin the body can't get glucose into the cells so it breaks down fat. That produces ketosis.

Don't eat any carbs: When we are not ingesting carbs, we burn body/ingested fat for energy & produce ketones. While physicians have often associated ketosis with unusual & unhealthy conditions (usual MD focus), staying in a chronic states of mild ketosis is quite healthy; strongly associated with healthier lipoprotein particle concentrations, low rates of diabetes, obesity, cardiovascular disease, cancer & mortality.