According to the Oregon State University webpage RENE DESCARTES (1595-1650), part of your question is explained by
Two months before the publication of the Passions Descartes set sail for Stockholm, Sweden, at the invitation of Queen Christina of Sweden. Descartes' death in Stockholm of pneumonia, has regularly been attributed to the rigours of the Swedish climate and the fact that Descartes (no early riser) was sometimes required to give the Queen lessons as early as five in the morning. However unpleasant these conditions may have been, it seems plain that Descartes acquired his fatal malady as a result of nursing his friend the French ambassador (who had pneumonia) back to health.
Similarly, according to the Washington and Lee University webpage RENÉ DESCARTES (1596-1650),
Because the Queen was often occupied with other business, and wanting to give full attention to philosophy, she arranged for her lessons to be at 5.00 a.m. René was staying at the French embassy opposite the Royal Palace, and had to take a carriage over the bridge to get to Palace each morning. He caught a cold, succumbed to a chill and died on the 11th February, 1650.
So, why did Descartes accept the offer from the Queen of Sweden and move to Stockholm? A possible answer is included in Stanford Encyclopedia of Philosophy webpage Descartes' Life and Works which suggests that the offer from Sweden came at a right to to allow him to get away from a situation that he felt was increasingly threatening his way of life. From the section of the Stanford website about Descartes The Passion, it becomes clear that a very tense and very public academic challenge to Descartes work was happening.
For many reasons, which would certanily include those related to his concerns about Voetius, Descartes accepted the offer
and went to Sweden. A decision, according to the Stanford document linked above, he began to have reservations about.