The trending hashtag was started by NHS Million, which is a campaign run unofficially by NHS staff to highlight the challenges faced by the service. They said: "We want all our NHS staff to feel the love this #ValentinesDay! Please tell the world the reasons why you #LoveYourNHS. Don't forget the hashtag!"
Earlier this month, US President Donald Trump sparked anger in the UK after claiming the NHS is "going broke and not working".
He claimed that the London demonstration "NHS in crisis: Fix it now", which called for increased funding to allow the NHS to meet the challenges posed by winter conditions, was evidence that the UK's universal healthcare system was not working.
Some of the stories told via #LoveYourNHS seem to prove the contrary, highlighting times the service has literally saved people's lives.
Some were heartwarming, including mum Jess who wrote: "Keeping me and my son alive during a horrific 84 hour labour and supporting me through the PTSD and post-natal depression that came after. We're both well and happy so a massive thank you to the NHS!"
Another parent, Jax, wrote: "After years of trying we had IVF on the NHS, worked first time, my wonderful, caring, compassionate daughter would not even exist without the NHS."
Others talked about the effect of cancer on their family's lives, saying they could not have got through it without the NHS. Marisa Chopino wrote: "My sis in law has been through chemo, had a double mastectomy plus reconstruction & now having radiotherapy. NO BILL to pay though, thank God."
The "free at the point of use" nature of the NHS also led to many comments. Toni, who used to work for the NHS, wrote: "The NHS doesn't leave people in lifelong debt after treatment. The NHS won't turn its back on you if you're poor. The NHS treats access to healthcare as a human right, and despite being under pressure, it's still one of the best healthcare systems in the world."
She added: "I've seen firsthand how much joint effort, care and perseverance goes in to providing quality healthcare. Doctors, nurses, midwives and NHS administrators are some of the most hardworking people I've ever met."
Here are a few more of the emotional stories shared on Valentine's Day: