SSRI "poop-out" is a thing that does happen (where the SSRI stops working), but that is usually a situation where you have maxed out the dosage and it still doesn't work, which is when you would look for a different med to replace the one that failed.
More common than "poop-out" is that your dose needs to be increased. Many of us are started on a lower SSRI dose anyway so increasing it isn't too big of a deal. Medication has given me my life back, but I did have a slip up where I thought the medication wasn't working for me any longer. Upping the dose worked great and solved the problem. I went from taking 50mg to 100mg of zoloft(sertaline) and felt normal again within a week or less.
More common than "poop-out" is that your dose needs to be increased. Many of us are started on a lower SSRI dose anyway so increasing it isn't too big of a deal. Medication has given me my life back, but I did have a slip up where I thought the medication wasn't working for me any longer. Upping the dose worked great and solved the problem. I went from taking 50mg to 100mg of zoloft(sertaline) and felt normal again within a week or less.