MariaDB (RDS) going temporarily offline (with memory drop)
Enable the slow query log to see what is going on: https://mariadb.com/kb/en/slow-query-log/
Running a fulltext index with a minimum token length of 1 also slows things down, if not necessary: https://mariadb.com/kb/en/innodb-system-variables/#innodb_ft_min_token_size