In this article we describe how well-being changed during 2020 in ten countries, namely Australia, Belgium, France, Germany, Great Britain, Italy, Luxembourg, New Zealand, South Africa, and Spain. Our measure of well-being is the Gross National Happiness (GNH), a country-level index built applying sentiment analysis to data from Twitter. Our aim is to describe how GNH changed during the pandemic within countries, to assess its validity as a measure of well-being, and to analyse its correlates. We take advantage of a unique data-set made of daily observations about GNH, generalized trust and trust in national institutions, fear concerning the economy, loneliness, infection rate, policy stringency and distancing. To assess the validity of data sourced from Twitter, we exploit various sources of survey data, such as Eurobarometer and consumer satisfaction, and big data, such as Google Trends. Results indicate that sentiment analysis of Tweets an provide reliable and timely information on well-being. This can be particularly useful to timely inform decision-making.