Haste is an incredibly useful buff in this edition: +2 AC, doubled movement rate, advantage on Dex saving throws, and a "cunning action" like free action that can even be used to Attack. It's a martial class's best friend, but has an important Achilles heel at the end of its description:
When the spell ends, the target can't move or take actions until after its next turn, as a wave of lethargy sweeps over it. – PHB p250
My question is whether something that suppresses the spell counts as an instance when the spell ends. This is particularly relevant to the Antimagic Field:
Spells. Any active spell or other magical effect on a creature or an object in the sphere [field] is suppressed while the creature or object is in it.- PHB p214
This question occurred to me when I was considering the role of spellcasters in a battle with a Beholder. The Beholder's antimagic field will not allow spellcasters to cast spells, but a spellcaster could still maintain concentration on a buff that they had cast when they were not yet in the field (according to http://www.sageadvice.eu/2016/06/14/how-do-you-rule-concentration-in-an-antimagic-field/). But I wondered if the Beholder would be able to trigger the lethargy by including the target of the spell in the field, perhaps even doing so repeatedly. For example, if a Wizard cast Haste on a Fighter, and then the Fighter was targeted by the antimagic field, what would happen?
Does a concentration spell count as the spell "ending" only when the spell is no longer being concentrated on, or does it also count when a spell temporarily stops having an effect?