The memory of our Righteous and God-bearing mother Ypomoni is celebrated on March 13th (the day of her repose) and May 29th (the date of the fall of Constantinople and the death of her son Constantine XI Palaiologos, according to: http://orthodoxwiki.org/Ipomoni_of_Loutraki)
St. Ypomoni, in the world Helen Dragash, and later as the wife of Manuel II Palaiologos, "Helen in Christ God Augusta and Empress of the Romans, Palaiologos", was the daughter of Constantine Dragash, one of the many leaders and inheritors of the large Serbian kingdom of Stefan Dusan. She came from royal and blessed generation. Many of her ancestors were Saints (e.g. Stefan Nemania. the Serbian king and founder of the Holy Monastery of Chilander on Mount Athos and St. Symeon the Myrrh-gusher). Konstantine Dragash assumed the leadership of what is today the Bulgarian portion of northeast Macedonia, in the area between the rivers Axiou and Strymonos. Her birth took place immediately after the death of the Dusan years. Her upbringing. education, and her treatment were greatly influenced by the Byzantine ideal, because the Serbs were greatly influenced by Byzantine culture. They thought of themselves as more identifying with the culture and especially the national consciousness of the Byzantine Empire. Emotionally and essentially they were considered Byzantine, as she was later allowed to become Augusta and Empress due to her birth in the Serbian homeland. Above and beyond these, she was raised with the family tradition of the unshakeable Orthodox faith in God. This faith guided and illumined her, and would inspire her life which would be full of sorrows and trials. She was about 19 years old when she married Manuel II Palaiologos (1390), a few days before becoming Emperor.
A recent miracle of the Saint
"Many are the appearances of St. Ypomoni in the last few years to the faithful and also to non-Christians. The following miraculous appearance involved the healing of a sick man.
St. Ypomoni appeared as a nun to a taxi driver from Athens. She stopped his taxi, and sought to be driven to Loutraki. The taxi driver had skin cancer on his hands and was experiencing a great lack of faith. On the way, the nun, who wore a cowl with a red cross asked him:
"Why are you sad?"
And he did not hesitate to confess the whole truth. After she asked him if he wanted her make the sign of the Cross on him so that he would become well, and he agreed. In a short time however, he started to get sleepy, and he asked the nun if they could stop for a little so that they wouldn't be killed. They had arrived close to the destination, and it would be easy for her to find another taxt. He stopped on the side of the road and fell asleep. When he woke up he noticed that his hands were better, but the nun had disappeared. He asked people in the area if they saw a nun near there, but no one had seen her. He therefore returned to his taxi and realized that it had been some Saint who had then disappeared. He headed right away to his doctor and related what had happened. At that instant his eyes fell on an icon which was hanging in the doctor's office, and he fell from his chair and cried:
"That was her."
The icon was of St. Ypomoni. Thus he learned who it was that healed him and softened his unbelief. The cowl with the red cross showed her origin before becoming Empress of Byzantium, and with this monastic schema her life ended. Later it became known that the day when the miracle occured was March 13th, the day when the Saint celebrates." (taken from: http://www.impantokratoros.gr/agiaypomoni.print.el.aspx)
(these hymns below are amateur translations)
Υπομονής θεοστηρίκτου την ομώνυμον και βασιλίδων θεοσόφων την υπέρτιμον, την εκλάμψασαν ως άστρον εν Βυζαντίω και χορούς μοναζουσών καταπυρσεύσασαν, ταπεινώσεως βολαίς ανευφημήσωμεν, πόθω κράζοντες. Χαίροις, Μήτερ πανεύφημε.