irrational
Irrational thoughts started swimming through his mind—he wanted to jump up and attack, beat him like he’d beaten Gaily after escaping the Maze. James Dashner  The Scorch Trials

not rational; i.e., lacking reason
More rarely, irrational numbers in mathematics are numbers that cannot be expressed as a fraction consisting of only an integer in the numerator and denominator. For example, pi is an irrational number while 1/3 is rational.
