Fast ion behaviour is central to burning plasma physics, auxiliary heating and current drive, and losses can cause significant plasma-wall interactions. Here fast ion losses on JET caused by plasma disruptions, TAE, fishbones are described. There are now several relevant diagnostics on JET: gamma-ray diagnostics, NPA, neutron spectrometry, Faraday Cups and a Scintillator Probe were used for simultaneous measurements of various species of confined and lost fast ions in the MeV energy range. The fast ion populations were generated in fusion reactions and were also produced by NBI and by accelerating with ICRH. Fast ion losses preceding disruptions were often detected by the Scintillator Probe in discharges with high bN. It was found that the losses are caused by the m = 2/n = 1 kink mode and these losses typically occur at the same time as the thermal quench, before the current quench that follows. A set of experiments was carried out where interactions of core-localised TAE modes with fast ions in the MeV energy range were studied in plasmas with monster sawteeth. Energy and pitch angle resolved SP measurements of MeV-ions ejected from the plasma due to fishbone oscillations driven by NBI-ions are also studied.